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Abstract: Occurring in the southwest of Western Australia, the 1968 Meckering earthquake (M S 6.8) resulted in the formation of an extensive surface rupture complex comprising faults with a range of orientations and reverse and dextral lateral offsets. Modeling of the seismological characteristics of the source showed that reverse failure occurred on a north–south striking, east-dipping surface, but how this is related to the local Precambrian bedrock geology is not clear. Interpretation of new aeromagnetic data has allowed concealed bedrock lithology and structure to be mapped in previously unachievable detail. These data show that the surface faulting correlates closely with linear magnetic anomalies, interpreted as dykes/faults and lithological contacts. The complicated pattern of surface faulting contrasts with the more simple seismological fault model, but can be explained in terms of the reactivation of northeasterly (dykes and faults) and northwesterly (stratigraphic) trending features in a stress regime with an east–west oriented maximum principal stress. Space problems created where these two trends converge led to the creation/reactivation of a linking north–south trending thrust fault which accommodated the greatest displacements recorded for the 1968 event. The district scale distribution of epicentres in the 3 years encompassing the Meckering event shows the same northeasterly and northwesterly trends as seen in the aeromagnetic data. The implied basement features controlling the seismicity will be prone to strike–slip failure in the regional, east–west oriented stress field. It is speculated that smaller events in the Meckering area will tend to be strike–slip and these account for most of the strain. Larger events, all known examples of which involve predominantly thrusting, are caused by stress build up where strike–slip faults with the two orthogonal trends intersect. This hypothesis provides an explanation for the lack of topography in the region, which is incompatible with the high level of seismic activity and a predominance of thrust faulting. [Copyright &y& Elsevier]

Abstract: A probabilistic neural network (PNN) is presented for predicting the magnitude of the largest earthquake in a pre-defined future time period in a seismic region using eight mathematically computed parameters known as seismicity indicators. The indicators considered are the time elapsed during a particular number () of significant seismic events before the month in question, the slope of the Gutenberg–Richter inverse power law curve for the events, the mean square deviation about the regression line based on the Gutenberg–Richter inverse power law for the events, the average magnitude of the last events, the difference between the observed maximum magnitude among the last events and that expected through the Gutenberg–Richter relationship known as the magnitude deficit, the rate of square root of seismic energy released during the events, the mean time or period between characteristic events, and the coefficient of variation of the mean time. Prediction accuracies of the model are evaluated using three different statistical measures: the probability of detection, the false alarm ratio, and the true skill score or R score. The PNN model is trained and tested using data for the Southern California region. The model yields good prediction accuracies for earthquakes of magnitude between 4.5 and 6.0. The PNN model presented in this paper complements the recurrent neural network model developed by the authors previously, where good results were reported for predicting earthquakes with magnitude greater than 6.0. [Copyright &y& Elsevier]

Abstract: We conducted a study of the spatial distributions of seismicity and earthquake hazard parameters for Turkey and the adjacent areas, applying the maximum likelihood method. The procedure allows for the use of either historical or instrumental data, or even a combination of the two. By using this method, we can estimate the earthquake hazard parameters, which include the maximum regional magnitude Mˆ max, the activity rate of seismic events and the well-known bˆ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. These three parameters are determined simultaneously using an iterative scheme. The uncertainty in the determination of the magnitudes was also taken into consideration. The return periods (RP) of earthquakes with a magnitude M≥m are also evaluated. The whole examined area is divided into 24 seismic regions based on their seismotectonic regime. The homogeneity of the magnitudes is an essential factor in such studies. In order to achieve homogeneity of the magnitudes, formulas that convert any magnitude to an M S -surface scale are developed. New completeness cutoffs and their corresponding time intervals are also assessed for each of the 24 seismic regions. Each of the obtained parameters is distributed into its respective seismic region, allowing for an analysis of the localized seismicity parameters and a representation of their regional variation on a map. The earthquake hazard level is also calculated as a function of the form Θ =(Mˆ max,RP 6.0), and a relative hazard scale (defined as the index K) is defined for each seismic region. The investigated regions are then classified into five groups using these parameters. This classification is useful for theoretical and practical reasons and provides a picture of quantitative seismicity. An attempt is then made to relate these values to the local tectonics. [Copyright &y& Elsevier]

Abstract: The rate of earthquake occurrence varies by many orders of magnitude in a given region due to variations in the stress state of the crust. Our focus here is on variations in seismicity rate triggered by transient aseismic processes such as fluid flow, fault creep or magma intrusion. While these processes have been shown to trigger earthquakes, converting observed seismicity variations into estimates of stress rate variations has been challenging. Essentially aftershock sequences often obscure changes in the background seismicity rate resulting from aseismic processes. Two common approaches for estimating the time dependence of the underlying driving mechanisms are the stochastic Epidemic Type Aftershock Sequence model (ETAS) [Ogata, Y., (1988), Statistical models for earthquake occurrences and residual analysis for point processes, J. Am. Stat. Assoc., 83, 9–27.] and a physical approach based on the rate- and state-model of fault friction [Dieterich, J., (1994), A constitutive law for rate of earthquake production and its application to earthquake clustering, J. Geophys. Res., 99, 2601–2618.]. The models have different strengths that could be combined to allow more quantitative studies of earthquake triggering. To accomplish this, we identify the parameters that relate to one another in the two models and examine their dependence on stressing rate. A particular conflict arises because the rate–state model predicts that aftershock productivity scales with stressing rate while the ETAS model assumes that it is time independent. To resolve this issue, we estimate triggering parameters for 4 earthquake swarms contemporaneous with geodetically observed deformation transients in various tectonic environments. We find that stressing rate transients increase the background seismicity rate without affecting aftershock productivity. We then specify a combined model for seismicity rate variations that will allow future studies to invert seismicity catalogs for variations in aseismic stressing rates. [Copyright &y& Elsevier]

We present a duration–amplitude procedure for rapid determination of a moment magnitude, Mwpd, for large earthquakes using P-wave recordings at teleseismic distances. Mwpd can be obtained within 20 min or less after the event origin time as the required data are currently available in near real time. The procedure determines apparent source durations, T0, from high-frequency, P-wave records, and estimates moments through integration of broad-band displacement waveforms over the interval tP to tP+ T0, where tP is the P-arrival time. We apply the duration–amplitude methodology to 79 recent, large earthquakes (global centroid-moment-tensor magnitude, MCMTw, 6.6–9.3) with diverse source types. The results show that a scaling of the moment estimates for interplate thrust and possibly tsunami earthquakes is necessary to best match MCMTw. With this scaling, Mwpd matches MCMTw typically within ±0.2 magnitude units, with a standard deviation of σ= 0.11, equaling or outperforming other approaches to rapid magnitude determination. Furthermore, Mwpd does not exhibit saturation; that is, for the largest events, Mwpd does not systematically underestimate MCMTw. The obtained durations and duration–amplitude moments allow rapid estimation of an energy-to-moment parameter Θ* used for identification of tsunami earthquakes. Our results show that Θ*≤−5.7 is an appropriate cut-off for this identification, but also show that neither Θ* nor Mw is a good indicator for tsunamigenic events in general. For these events, we find that a reliable indicator is simply that the duration T0 is greater than about 50 s. The explicit use of the source duration for integration of displacement seismograms, the moment scaling and other characteristics of the duration–amplitude methodology make it an extension of the widely used, Mwp, rapid magnitude procedure. The need for a moment scaling for interplate thrust and possibly tsunami earthquakes may have important implications for the source physics of these events. [ABSTRACT FROM AUTHOR]

Abstract: Teleseismic Broadband seismograms of P-waves from the May 1990 southern Sudan and the December, 2005 Lake Tanganyika earthquakes; the western branch of the East African Rift System at different azimuths have been investigated on the basis of magnitude spectra. The two earthquakes are the largest shocks in the East African Rift System and its extension in southern Sudan. Focal mechanism solutions along with geological evidences suggest that the first event represents a complex style of the deformation at the intersection of the northern branch of the western branch of the East African Rift and Aswa Shear Zone while the second one represents the current tensional stress on the East African Rift. The maximum average spectral magnitude for the first event is determined to be 6.79 at 4s period compared to 6.33 at 4s period for the second event. The other source parameters for the two earthquakes were also estimated. The first event had a seismic moment over fourth that of the second one. The two events are radiated from patches of faults having radii of 13.05 and 7.85km, respectively. The average displacement and stress drop are estimated to be 0.56m and 1.65MPa for the first event and 0.43m and 2.20MPa for the second one. The source parameters that describe inhomogeneity of the fault are also determined from the magnitude spectra. These additional parameters are complexity, asperity radius, displacements across the asperity and ambient stress drop. Both events produce moderate rupture complexity. Compared to the second event, the first event is characterized by relatively higher complexity, a low average stress drop and a high ambient stress. A reasonable explanation for the variations in these parameters may suggest variation in the strength of the seismogenic fault which provides the relations between the different source parameters. The values of stress drops and the ambient stresses estimated for both events indicate that these earthquakes are of interplate type. [Copyright &y& Elsevier]

• One month long seismic sequence, with several large (M w + 6.2) events. • Combination of seismic and aseismic slip in an area of intermediate coupling. • Migration of slip sustained by the aftershock seismicity. • This migration leads to the triggering of the M w 6.4 aftershock after 17 h. • Unusually large postseismic displacements (aseismic and rapid afterslip). An earthquake sequence occurred in the Atacama region of Chile throughout September 2020. The sequence initiated by a mainshock of magnitude M w = 6.9, followed 17 hours later by a M w = 6.4 aftershock. The sequence lasted several weeks, during which more than a thousand events larger than M l = 1 occurred, including several larger earthquakes of magnitudes between 5.5 and 6.4. Using a dense network that includes broad-band, strong motion and GPS sites, we study in details the seismic sources of the mainshock and its largest aftershock, the afterslip they generate and their aftershock, shedding light of the spatial temporal evolution of seismic and aseismic slip during the sequence. Dynamic inversions show that the two largest earthquakes are located on the subduction interface and have a stress drop and rupture times which are characteristics of subduction earthquakes. The mainshock and the aftershocks, localized in a 3D velocity model, occur in a narrow region of interseismic coupling (ranging 40%-80%), i.e. between two large highly coupled areas, North and South of the sequence, both ruptured by the great M w ∼ 8.5 1922 megathrust earthquake. High rate GPS data (1 Hz) allow to determine instantaneous coseismic displacements and to infer coseismic slip models, not contaminated by early afterslip. We find that the total slip over 24 hours inferred from precise daily solutions is larger than the sum of the two instantaneous coseismic slip models. Differencing the two models indicates that rapid aseismic slip developed up-dip the mainshock rupture area and down-dip of the largest aftershock. During the 17 hours separating the two earthquakes, micro-seismicity migrated from the mainshock rupture area up-dip towards the epicenter of the M w 6.4 aftershocks and continued to propagate upwards at ∼ 0.7 km/day. The bulk of the afterslip is located up-dip the mainshock and down-dip the largest aftershock, and is accompanied with the migration of seismicity, from the mainshock rupture to the aftershock area, suggesting that this aseismic slip triggered the M w = 6.4 aftershock. Unusually large post-seismic slip, equivalent to M w = 6.8 developed during three weeks to the North, in low coupling areas located both up-dip and downdip the narrow strip of higher coupling, and possibly connecting to the area of the deep Slow Slip Event detected in the Copiapo area in 2014. The sequence highlights how seismic and aseismic slip interacted and witness short scale lateral variations of friction properties at the megathrust. [ABSTRACT FROM AUTHOR]

Abstract: We have analysed three recent earthquake sequences in the northern part of the Taupo Volcanic Zone. A 1998 sequence at Haroharo with a largest event of M L 4.8, and a 2004 sequence near Lake Rotoehu (largest event M L 5.4), had normal b-values, and displayed an aftershock decay pattern, with most of the activity within the first few days. In contrast, a 2005 sequence a few tens of kilometres away at Matata (largest event M L 4.1), had very different characteristics, with a slow development and decay, no tendency for enhanced seismicity after the larger events, and a very high b-value. The focal mechanisms of the Rotoehu and Matata events are normal, and have stress patterns consistent with the geodetically observed extension of the Taupo Volcanic Zone in a northwest–southeast direction. The extensive recent volcanism in the Okataina Volcanic Centre does not seem to have affected the stress pattern in this area. The Rotoehu sequence showed a strong resemblance, particularly in the time distribution of events, to the well-known swarm activity in the Vogtland region on the German/Czech border, in which larger events were followed by a burst of seismicity, as in a normal aftershock sequence. Some of the arguments that have been advanced to explain the Vogtland swarm as seismicity induced by fluid injection apply to Rotoehu, but there is no direct evidence of fluid involvement. The Matata sequence appears to have a continuing trigger mechanism, either a slow injection of fluid, or a slow slip event, in an environment in which opening pore spaces prevent high overpressures developing. The Matata sequence occurred close to the area of the 1987 M L 6.3 Edgecumbe Earthquake, so exhibiting two extremes of seismic temporal pattern, namely mainshock–aftershock and a swarm with many events of similar magnitude, within a small area. [Copyright &y& Elsevier]

Using the P-wave magnitude spectra of the vertical component of teleseismic broadband seismograms, average source parameters have been retrieved for five significant earthquakes of Mw ⩾ 5.7 occurring in Egypt namely, 1992 Cairo earthquake, 1998 Alexandria earthquake and three events which occurred in the Gulf of Aqaba region between 1993 and 1995. The magnitude spectrum represents the velocity amplitude density spectrum at the earthquake source, scaled in magnitude units. The maximum of the magnitude spectrum along with the period at which the maximum occurs are used to estimate the source parameters. For precise determination of the source parameters, two different methods for deriving the corner periods are applied. The obtained source parameters were compared with those derived in previous studies. The results show that within the moment magnitude range 5.5 ~ 7.2, the corner periods are 1.29 ~ 11.6 s, length of the fault ruptures are 5.5 ~ 50 km and the stress drops are 0.5 ~ 4.8 MPa. The derived stress drop shows an increasing trend with the seismic moment for the three Gulf of Aqaba earthquakes. The 1995 Gulf of Aqaba earthquake of Mw = 7.2, the largest earthquake to have occurred in Egypt in the last century is characterized by a higher complexity compared to the other events, that are much simpler. The values of the corner periods for this earthquake are azimuth dependent due to complexity and strong directivity of its rupture. For a detailed description of the complexity of 1995 earthquake additional source parameters are also estimated in terms of an inhomogeneous source model. These parameters are the asperity radius, displacement across the asperity, localized stress drop and ambient faulting stress. The average stress drop of Cairo, 1992 and Alexandria, 1998 intraplate earthquakes shows larger values compared with the interplate 1993 Gulf of Aqaba earthquakes. Generally, the estimated seismic moment using the magnitude spectra reflect good agreement with the estimates made from the other techniques for simple source while the complex source yields smaller values. [ABSTRACT FROM AUTHOR]

Abstract: The development and implementation of an earthquake early warning system (EEWS), both in regional or on-site configurations can help to mitigate the losses due to the occurrence of moderate-to-large earthquakes in densely populated and/or industrialized areas. The capability of an EEWS to provide real-time estimates of source parameters (location and magnitude) can be used to take some countermeasures during the earthquake occurrence and before the arriving of the most destructive waves at the site of interest. However, some critical issues are peculiar of EEWS and need further investigation: (1) the uncertainties on earthquake magnitude and location estimates based on the measurements of some observed quantities in the very early portion of the recorded signals; (2) the selection of the most appropriate parameter to be used to predict the ground motion amplitude both in near- and far-source ranges; (3) the use of the estimates provided by the EEWS for structural engineering and risk mitigation applications. In the present study, the issues above are discussed using the Campania–Lucania region (Southern Apennines) in Italy, as test-site area. In this region a prototype system for earthquake early warning, and more generally for seismic alert management, is under development. The system is based on a dense, wide dynamic accelerometric network deployed in the area where the moderate-to-large earthquake causative fault systems are located. The uncertainty analysis is performed through a real-time probabilistic seismic hazard analysis by using two different approaches. The first is the Bayesian approach that implicitly integrate both the time evolving estimate of earthquake parameters, the probability density functions and the variability of ground motion propagation providing the most complete information. The second is a classical point estimate approach which does not account for the probability density function of the magnitude and only uses the average of the estimates performed at each seismic station. Both the approaches are applied to two main towns located in the area of interest, Napoli and Avellino, for which a missed and false alarm analysis is presented by means of a scenario earthquake: an M 7.0 seismic event located at the centre of the seismic network. Concerning the ground motion prediction, attention is focused on the response spectra as the most appropriate function to characterize the ground motion for earthquake engineering applications of EEWS. [Copyright &y& Elsevier]

We present new paleoseismicity data for the 30 km long and 2.5 m high Hyden fault scarp in Western Australia, which, when combined with the results of previous research, provides the most extensive record of surface-rupturing earthquakes yet assembled for an 'active' Australian intracratonic fault. The data indicate that four to five surface-rupturing earthquakes have occurred on the Hyden Fault during the Quaternary (E1, ca 20 ka; E2, ca 55 - 50 ka; E3, ca 100 - 90 ka; and two events E4 and E5, >200 ka). Activity is episodic, with single seismic cycle slip rates varying from 0.03 mm/y to <0.01 mm/y. Paleo-earthquake magnitudes are estimated to have been in the order of Mw 6.8. The identification of a similar fault scarp immediately northwest of the Hyden scarp, and of two airphoto lineaments to the west of the Hyden scarp, indicates that strain is distributed among a family of faults in this region. The presence of multiple nearby active faults suggests that the recurrence of severe ground shaking in the Hyden region is more frequent than indicated by the paleoseismic data presented here. [ABSTRACT FROM AUTHOR]

Aftershock sequences of the magnitude M W =6.4 Bingöl earthquake of 1 May, 2003 (Turkey) are studied to analyze the spatial and temporal variability of seismicity parameters of the b value of the frequency-magnitude distribution and the p value describing the temporal decay rate of aftershocks. The catalog taken from the KOERI contains 516 events and one month’s time interval. The b value is found as 1.49 ± 0.07 with Mc =3.2. Considering the error limits, b value is very close to the maximum b value stated in the literature. This larger value may be caused by the paucity of the larger aftershocks with magnitude M D ≥ 5.0. Also, the aftershock area is divided into four parts in order to detect the differences in b value and the changes illustrate the heterogeneity of the aftershock region. The p value is calculated as 0.86 ± 0.11, relatively small. This small p value may be a result of the slow decay rate of the aftershock activity and the small number of aftershocks. For the fitting of a suitable model and estimation of correct values of decay parameters, the sequence is also modeled as a background seismicty rate model. Constant background activity does not appear to be important during the first month of the Bingöl aftershock sequences and this result is coherent with an average estimation of pre-existing seismicity. The results show that usage of simple modified Omori law is reasonable for the analysis. The spatial variability in b value is between 1.2 and 1.8 and p value varies from 0.6 to 1.2. Although the physical interpretation of the spatial variability of these seismicity parameters is not straightforward, the variation of b and p values can be related to the stress and slip distribution after the mainshock, respectively. The lower b values are observed in the high stress regions and to a certain extent, the largest b values are related to Holocene alluvium. The larger p values are found in some part of the aftershock area although no slip occurred after the main shock and it is interpreted that this situation may be caused by the alluvium structure of the region. These results indicate that the spatial distribution in b and p values are generally related to the rupture mechanism and material properties of an aftershock area. [ABSTRACT FROM AUTHOR]

A wide variety of near-fault strong ground motion records were collected from various tectonic environments worldwide and were used to study the peak value ratio and response spectrum ratio of the vertical to horizontal component of ground motion, focusing on the effect of earthquake magnitude, site conditions, pulse duration, and statistical component. The results show that both the peak value ratio and response spectrum ratio are larger than the 2/3 value prescribed in existing seismic codes, and the relationship between the vertical and horizontal ground motions is comparatively intricate. In addition, the effect of the near-fault ground motions on bridge performance is analyzed, considering both the material nonlinear characteristics and the P∼Δ effect. [ABSTRACT FROM AUTHOR]

We examine seismic waveforms generated by clusters of similar earthquakes and additional events located on the Karadere–Duzce branch of the North Anatolian fault to investigate possible scaling between proposed early signals in the P waveforms and magnitudes. The employed signals can be divided into two classes. The first is associated with Ellsworth–Beroza and Iio type signals that are assumed to reflect signatures of seismic nucleation phases. The second are associated with Nakamura type period and Wu–Zhao type maximum displacement in the early waveforms that are related to measures of the corner frequency and local magnitude, respectively. The impact on each signal of artefacts generated by the Finite Impulse Response (FIR) filter is also examined. The use of repeating event clusters reduces considerably the variability of path and site effects compared to previous regional and global studies. This allows us to focus more accurately on variations of the potential scaling parameters with the source magnitude. However, the magnitude range of the employed events is limited to about 4 units. The FIR filter artefacts can generate spurious signals prior to the P-wave arrival, potentially affecting the Ellsworth–Beroza type signals, but are not a significant influence on any of the other measurements. The results indicate that candidates for the Ellsworth–Beroza signals, associated with identification of a weak arrival before the main P phase, exist in less than 20 per cent of the cases. The Iio type signals can be determined by definition on all waveforms. Both of these potential signatures of nucleation phases show little or no scaling with the final event size in the examined data. In contrast, the Nakamura and Wu–Zhao type signals in the first few seconds, which can also be determined by definition on all waveforms, appear to scale with the final event magnitude, albeit with large scatter. The relatively large time windows used in the analysis, compared to the rupture time of the employed events, implies that the results provide little if any information on the physical process of the rupture initiation. The scaling of the Nakamura and Wu–Zhao type early signals with the final event size may be explained by statistical tendency of stronger initial rupture phases to propagate larger distances. [ABSTRACT FROM AUTHOR]

Abstract: To clarify differences in the maximum magnitude of interplate earthquakes offshore of Shikoku (≈ M 8) and in the western adjacent Hyuganada region (≤ M 7.5), southwest Japan, where the oceanic Philippine Sea (PHS) plate subducts beneath the continental Amuria plate along the Nankai Trough, we calculated the temperature distribution for the plate interface using a three-dimensional thermal convection model. We attribute the observed very low heat flow values (less than approximately 45 mW/m2) in the southern part of the Hyuganada region to the subduction of the Kyushu–Palau Ridge, which is presumably older than the adjacent Shikoku Basin to the east. Trial and error methods suggest an age difference of about 20 Myr between these two areas. The heat flow calculated from the temperature distribution fits the observed heat flow in the Hyuganada region well. The results show that Hyuganada earthquakes may take place in the newly proposed “Hyuganada triangle,” bounded by a southeastern isotherm of about 200 °C on the plate interface, a northwestern boundary between the upper surface of the subducting PHS plate and the continental Moho discontinuity, a northern isotherm of about 350 °C, and a northeastern margin-normal zone with a possible barrier or large friction parameter L. Interplate earthquakes in such a limited seismogenic zone may reach a maximum magnitude of M 7.5. Our results also suggest that a seismic gap seaward of the Hyuganada region may be caused by stable sliding arising from low temperature, resulting in a deeper updip limit than that offshore of Shikoku. The seismic gap offshore southwest of southern Kyushu along the Ryukyu Trench may result from the overlapping of two stable sliding regimes on the plate interface: one with low temperature at shallower depths caused by the subduction of the old PHS plate and the other a serpentinized mantle wedge at deeper depths. [Copyright &y& Elsevier]

Distributions of time between consecutive earthquakes verify an approximately universal scaling law for stationary seismicity. The shape of these distributions is shown to arise as a mixture of one distribution for short-distance events and an exponential distribution for far-off events, the distinction from short and long distances being relative to the size of the region studied. The distributions of consecutive distances show a double power law decay and verify an approximate scaling law which guarantees the simultaneous fulfillment of the scaling laws for time. The interplay between space and time can be seen as well by looking at the distribution of distances for a fixed time separation. These results suggest that seismicity can be understood as a series of intertwined independent continuous-time random walks, with power law-distributed waiting times and Lévy-flight jumps. However, a simple model based on these ideas does not capture the invariance of seismicity under renormalization. [ABSTRACT FROM AUTHOR]

At the Koyna reservoir in western India, it is observed that earthquakes of magnitude (M) 4-5 are often preceded by well-defined clusters of foreshocks of M ≤ 3, referred to as nucleation that is found to last typically for 100-400 h. Based on continuous monitoring of seismic activity, a nucleation pattern was identified and an earthquake of M 4+ was forecasted on 16 May 2006. An earthquake of M 4.2 did occur on 21 May 2006 within the forecasted parameters. The continued seismic activity in such an isolated and well-monitored site probably makes Koyna a suitable locale to pursue meaningful study of earthquake precursors. [ABSTRACT FROM AUTHOR]

We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from and the peak ground-motion velocity ( PGV) from Pd. The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P-wave trigger is constantly monitored. When a trigger occurs, and Pd are computed. We found the relationship between and magnitude ( M) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds. [ABSTRACT FROM AUTHOR]

We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990-1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake. [ABSTRACT FROM AUTHOR]

Peninsular India (PI), which lies south of 24°N latitude, has experienced several devastating earthquakes in the past. However, very few strong motion records are available for developing attenuation relations for ground acceleration, required by engineers to arrive at rational design response spectra for construction sites and cities in PI. Based on a well-known seismological model, the present paper statistically simulates ground motion in PI to arrive at an empirical relation for estimating 5% damped response spectra, as a function of magnitude and source to site distance, covering bedrock and soil conditions. The standard error in the proposed relationship is reported as a function of the frequency, for further use of the results in probabilistic seismic hazard analysis. [ABSTRACT FROM AUTHOR]

There is a fundamental connection between crustal strain (deformation) rates and seismic activity. To this end two FORTRAN utility programs have been developed, aimed at estimating the seismicity on a fault in cases when this cannot be done directly, or as a comparison with observed data. The first program (“moment_slip”) is one in which seismicity is derived from the rate of seismic slip, based on published models for the connection between slip rates and seismic activity. The size of the fault is essential here, constraining the maximum magnitude. The slope of the frequency–magnitude distribution and its functional form are other important controlling parameters. The key physical concept in this connection is seismic moment release, which is related to magnitude through specified moment–magnitude relationships. For cases when slip rates are not available a second program (“moment_rate”) has been developed, aimed at computing the recurrence rate from an estimate of the moment release, inferred for example from historical and/or recent seismicity in the region in which the fault is located. A number of sensitivity tests demonstrate the relative importance of the different assumptions and parameters. [Copyright &y& Elsevier]

We have derived, evaluated, and compared two empirical methods for computing duration magnitude M D from 25 short-period vertical component stations of the Northern Morocco Seismic Network (NMSN). M D has been scaled to IGN (Insituto Geograpfico National, Spain) body-wave magnitude (mb IGN ), using a set of 479 shallow (less than 30 km) earthquakes recorded from March 1992 to February 2001, with 2.5 ≤ mb IGN ≤ 5.4. In the first approach: Individual Network Calibration, we determined an individual M D formula for each station. In the second approach: Global Network Calibration, we used a single relationship to compute M Dij (from the jth observation for the i-th earthquake) magnitudes at 25 selected stations as: M Dij = − 0.14 +1.63 log10 (τ ij )+0.031(Δ ij)+ cSta j . Residuals ( M Dij − mb IGN ) for both techniques were thereafter deduced. Comparison between the two approaches provided the principal results: (1) The mean correlation between estimated magnitude; M Dij and reference magnitude; mb IGN is about 89.9% for the individual calibration method, and near 95% for global calibration method in which station corrections cSta j were introduced, (2) Residuals ( M Dij − mb IGN ) are relatively large, and are ranging between − 0.60 and 0.60 magnitude units, for the individual calibration method, whereas they vary in the range − 0.38 to 0.40, for the global calibration method with corrections; cSta j . (3) A random distribution of residuals ( M Dij − mb IGN ) is observed for each station in the case of the individual approach. Thus, the resulting average of these residuals is almost equal to zero. Using a global calibration without corrections results in negative residuals for a group stations and positive residuals for another an group indicating respectively that sites corresponding to these groups have a tendency to underestimate, or overestimate observed magnitude values. [ABSTRACT FROM AUTHOR]

For the Fiji-Tonga-Kermadec area and for the period from January 1977 to July 2003, the Harvard CMT catalogue lists 1022 shallow, 410 intermediate and 633 deep earthquakes of moment magnitude from 4.9 to 8.0. The magnitude threshold, above which the catalogue is complete, is 5.3–5.4, and the number of earthquakes of magnitude above this value is 691 for shallow, 329 for intermediate and 476 for deep events, respectively. The proportion of earthquakes associated with doublets and multiplets against the total number of earthquakes is approximately the same in both data sets and therefore all earthquake pairs were considered regardless of their magnitude. We investigated all the pairs of earthquakes that occurred at a centroid distance of less than 40, 60 or 90 km from each other and within a time interval of 200, 300 or 450 days, depending on their magnitude. We found 208 pairs of shallow, 31 of intermediate and 92 of deep events. To ascertain whether these earthquakes in pairs are not connected by chance, the possibility of their occurrence in an uncorrelated Poissonian catalogue was considered. It was assumed that in such a catalogue the inter-event time is exponentially distributed, the earthquake magnitude follows the Gutenberg-Richter relation, and the distribution of centroid distances between the events in pairs is controlled by its non-parametric kernel estimate. The probability of the appearance of the observed proportion of doublets of shallow earthquakes in the Poissonian catalogue was found to be very low. The low probability of occurrence in a semi-random catalogue, created by randomising centroid locations in the actual data set, also indicates major importance of the distance criterion used for a doublet specification. In general, shallow earthquakes tend to form pairs at shorter distances and within shorter time intervals than deep earthquakes. Both the distance and the time intervals do not depend on the magnitude of involved events. The largest number of pairs of deep earthquakes is observed at a depth of about 600 km, and the proportion of deep events associated with doublets against the number of all events increases with depth. From comparison of the focal mechanism of earthquakes in pairs, measured by the 3-D rotation angle, it follows that deep earthquakes forming pairs have a more diverse focal mechanism than shallow events; the rotation angle for three quarters of shallow pairs and only for about one third of deep pairs is reasonably small. The azimuth between two events forming a doublet is in about 60–65% of cases close to the strike of one of nodal planes of the first or the second event. [ABSTRACT FROM AUTHOR]

The article presents a study which provides evidence that the ultimate size of a seismic rupture is largely controlled by the structure of the underlying fault which gives the conclusion that big earthquakes do not differ from small earthquakes in their beginnings. The data in the study seem to conflict with earlier observations that the size of an earthquake is deterrmined by the dynamics of rupture onset.

Abstract: This paper shows an evaluation of the seismic activity in the entrance of the Gulf of Suez using the data recorded by Hurghada Seismological Network (HSN), in the period between August 1994 and December 1997 and represents an extension for the work published by the previous investigators. Hypocentral locations were determined for 180 earthquakes (duration magnitude ranged between 1.6 and 4.3) selected from 300 recorded events. All these events are located with epicentral error and depth error of less than 2km. The spatial distribution of these earthquakes indicates the presence of three active areas. These are Shadwan Island, Gubal Island and the area adjacent to the southern tip of Sinai Peninsula. Such pattern of activity implies a localization of stress below these areas. The concentration of the stress field in these areas may have been strongly controlled by ductile necking and or intrusion. Composite fault plane solutions were also constructed for each of the three active areas. The data for each area was divided into groups, according to geographical position and uniformity of polarity data. In Shadwan Island, the composite fault plane solution of 15 events shows almost pure dip-slip motion. The composite fault plane solutions in Gubal Island and the area adjacent to the southern tip of Sinai Peninsula indicate a mixed regime of both strike-slip and extensional faulting mechanisms. The stress regime obtained from the fault plane solutions in this study is predominantly NNE–SSW tensional stress field. This result is consistent with the present day stress field, which has a 010°±18° orientation. The overall results are correlated with the structural setting of the area known from other sources. [Copyright &y& Elsevier]

Abstract: In the Kanto region, there have been reports of decreasing b-values prior to earthquakes (M ≥5.5). The change of b-values is defined as the difference between the long- and short-term average earthquake magnitudes. A hazard function for moderately large earthquakes has also been proposed. This model was based on earthquakes that occurred between 1982 and 1999, and its effectiveness is measured retrospectively. In order to evaluate the effectiveness of the model through the use of independent data, the verification test is based on earthquakes observed after January 2000. Through the end of 2004, the only event where there was a decrease in mean event size was observed on June 3, 2000. This decrease resulted in a log-likelihood for the proposed model 1.3 units larger than that of the Poisson model, supporting the validity of the proposed model. Without accumulating further examples, we attempted to improve the verification test by expanding the study volume and by lowering the target cutoff magnitude in order to overcome the small sample size. When two other targets from the expanded volume were added, the difference in the log-likelihood (ΔlnL) increased to 3.6. In this case, the information rate per event was about 1.2, larger than that of the model period. Lowering the cutoff magnitude increased ΔlnL to 2.5. These extended tests led to higher confidence in the model with the larger ΔlnL value than did the primary test. From the viewpoint of the per-event information rate, each case involving targets with a magnitude 5.5 and larger resulted in better performance than in the model period. [Copyright &y& Elsevier]

The seismic safety of city gas supply has been the major research topic of the writers in past decades. To avoid earthquake hazards due to leakage of gas from breakage of buried pipes, a real-time safety control system, SUPREME, has been deployed and put into practical use. SUPREME employs 3,800 new spectrum intensity sensors and remote control devices to achieve quick gas supply shut off. It monitors the earthquake motion at a large number of sites on a real-time basis, interprets the data, and assesses gas pipe damage in order to decide whether or not the gas supply should be interrupted. The present paper first describes the philosophy behind this system. Second, it describes the performance of the system during the recent Taiwan earthquakes as well as more significant design earthquakes. This system represents the state-of-the-art of computer-operated safety measures, achieved by advanced geotechnical engineering. [ABSTRACT FROM AUTHOR]

Located some 90 km north of the town of Sept-Îles, Quebec, the Sainte-Marguerite-3 (SM-3) hydroelectric project was one of the most ambitious in eastern North America in recent years. The project included the construction of a 171 m high dam that created a 140 km long reservoir, some 120 m deep near the dam toe. Although the reservoir is located in a weakly seismic area of the Canadian Shield, reservoir-induced earthquakes occurred. A first event (mN 1.3) was recorded in September 1999, ~17 months after the reservoir started filling. Between October 2000 and March 2001, four additional events were detected by the Canadian National Seismograph Network, the largest being mN 1.7. During a field survey that took place between July and October 2001, 276 events of magnitude mN ≤ 1.2 were detected within 30 km of a three-component seismograph. Single-station locations, confirmed by agreement between P phase and S phase azimuths, were determined for 182 events. Most earthquakes fall in four areas with estimated focal depths mostly shallower than 2 km. Since the field survey completion, more events have taken place, but the largest one is mN 2.2 as of March 2006. This paper presents a detailed analysis of the reservoir-triggered events, together with a summary of seismic hazard evaluation of the dam site, the seismic parameters selected for dynamic analysis, and the selection of the design earthquake. [ABSTRACT FROM AUTHOR]

Seismic hazard in terms of spectral acceleration ( SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration ( PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra ( UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 ( M S 6.8), and October 10, 1980 ( M S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The Elat fault (a segment of the Dead Sea Transform) runs along the southern Arava valley (part of the Dead Sea Rift, Israel) forming a complex fault zone that displays a time-dependent seismic behaviour. Paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than M 6 during the late Pleistocene and the Holocene. However, at present the Elat fault is one of the quietest segments of the Dead Sea Transform, lacking even microsesimicity. The last event detected in the southern Arava valley occurred in the Avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south. Paleoseismological, geophysical and archaeological evidences indicate that this event was the historical devastating earthquake, which occurred in 1068 AD in the eastern Mediterranean region. According to the present study this event was strong enough to rupture the surface, reactivate at least two fault branches of the Elat fault and vertically displace the surface and an early Islamic irrigation system by at least 1 m. In addition, the playa area was uplifted between 2.5 and 3 m along the eastern part of the Elat fault shear zone. Such values are compatible with an earthquake magnitude ranging between M 6.6 and 7. Since the average recurrence interval of strong earthquakes during the Holocene along the Elat fault is about 1.2±0.3 ky and the last earthquake occurred more about 1000 years ago, the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards. [Copyright &y& Elsevier]

On September 7, 1999 an earthquake with magnitude MW = 5.9 occurred close to the city of Athens in Greece. More than 80 buildings collapsed, about 150 deaths and hundreds of injuries were reported. Soon after the event a damage investigation was carried out by two of the authors in the most heavily struck areas. The most serious damages were observed in the northern suburbs of Athens, where reinforced concrete frames and masonry buildings represent the prevalent construction systems. The hysteretic energy demands imposed on RC buildings should have been rather severe considering the structural systems characteristics and the inadequate construction details. However, overstrengths, redundancy and especially the presence of infill walls, provided a significant increase of the seismic capacity and contributed to the survival of many buildings. The objective of the present work is to reproduce and analyse the response of typical RC frames subjected to the 1999 Athens earthquake in areas where the observed damage was particularly severe but no recordings of the ground motion were available. After a general overview of the seismotectonic environment, seismological data, observed macroseismic intensities, structural typologies and observed building behaviour, an attempt is made to identify representative excitations in the meizoseismal area. Specifically, the required accelerograms are obtained by modifying available records so as to reproduce a given global energy content and to be consistent with the observed damage. To study the seismic response of RC models, the obtained accelerograms are used to perform nonlinear dynamic analyses. [ABSTRACT FROM AUTHOR]

Abstract: In this study, historical and seismotectonic data from the broader Aegean region, which are relevant to liquefaction phenomena, have been collected in order to investigate the relationship between epicentral (R e) and fault (R f) distance versus magnitude. Initially, a preliminary catalogue of sites where liquefaction induced ground failures or structural damages is presented. These liquefaction case histories have been triggered by 88 earthquakes since 1509. Based on these data, an upper bound of maximum epicentral distance (R emax) for a given earthquake magnitude M s is calculated. The corresponding equation is M s =4.742+4.655×10−3 R emax +0.8907log(R emax). This curve fits well with those proposed by previous studies and shows that the epicentral distance increases along with increasing magnitude. The lower limit of earthquake magnitude that induced liquefaction within the study area is M s =5.0, while the upper limit is M s =7.6. Furthermore, the closest distance of the liquefied sites to the causative faults was estimated in order to determine a distance–magnitude relation and to give numerical results for seismic hazard assessment. The calculated regression that is suggested is: M s =5.224+7.34×10−3 R fmax +0.488log(R fmax) for 5.5≤ M s ≤7.1 and it concerns normal faulting data. The strike-slip faulting data were few and the attempt to estimate regression for this category of faulting was unsuccessful. Moreover, the distribution of data reported to the instrumental era (after 1900) indicates that there is a rise in the values of the epicentral distance of liquefied sites triggered by earthquakes of magnitudes M s >6.6. The equation of the best-fit curve based on these data is: M s =0.01R e +6.463±0.46. In addition, an attempt was made to calculate regressions of R e on M s, according the focal mechanism of the event. In what concerns the normal faulting data, the equation of the best-fit curve and the upper bound curve are M s =0.01R e +6.38±0.38 and M s =0.021R emax +5.3, respectively, for M s values between 5.5 and 7.1. [Copyright &y& Elsevier]

A formula to determine the local magnitude (M L) following Richter’s original definition was empirically derived for the Korean Peninsula. A total of 1,644 digital seismograms from 142 Korean earthquakes that occurred from 1997 to 2000 were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response to be appropriate for the original definition ofM L. Then, the zero-to-peak amplitude was measured in millimeters on the synthetic Wood-Anderson seismogram. Multiple regression analysis was conducted to determine distance and station correction terms for the measured peak amplitudes. The best-fit solution forM L yielded the following formula for the Korean Peninsula:whereA(?) andSdenote the peak amplitude on the synthetic Wood-Anderson seismogram at distance ? and the station correction term, respectively. Note that the second term, distance correction, was adjusted with Richter’sM L, taking into consideration attenuation differences between the Korean Peninsula and southern California, where Richter originally introducedM L. On average, the magnitudes determined in this study are nearly the same as those determined by the Korea Institute of Geoscience and Mineral Resources (KIGAM), but are larger than those of the Korea Meteorological Administration (KMA) by as much as 0.36. [ABSTRACT FROM AUTHOR]

East Pacific Rise transform faults are characterized by high slip rates (more than ten centimetres a year), predominately aseismic slip and maximum earthquake magnitudes of about 6.5. Using recordings from a hydroacoustic array deployed by the National Oceanic and Atmospheric Administration, we show here that East Pacific Rise transform faults also have a low number of aftershocks and high foreshock rates compared to continental strike-slip faults. The high ratio of foreshocks to aftershocks implies that such transform-fault seismicity cannot be explained by seismic triggering models in which there is no fundamental distinction between foreshocks, mainshocks and aftershocks. The foreshock sequences on East Pacific Rise transform faults can be used to predict (retrospectively) earthquakes of magnitude 5.4 or greater, in narrow spatial and temporal windows and with a high probability gain. The predictability of such transform earthquakes is consistent with a model in which slow slip transients trigger earthquakes, enrich their low-frequency radiation and accommodate much of the aseismic plate motion. [ABSTRACT FROM AUTHOR]

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years'' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years'' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels. [Copyright &y& Elsevier]

The mechanisms generating the charges/potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational, theoretical and laboratory studies, in particular over the last few decades. We previously conducted stick-slip tests using precut granite cores with a contact electrode on the sample side, and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above-mentioned charges or potentials. Here we discuss seismo-electric and magnetic fields formed by the surface charges, and derive their scaling laws with the earthquake magnitude at a distance. According to our model, detectability of these fields at a point on the ground surface depends strongly on wet/dry condition at a fault zone (sheared asperities). Terra Nova, 00, 1–5, 2004 [ABSTRACT FROM AUTHOR]

We produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the European-Mediterranean region. The procedure automatically screens near real-time earthquake alerts provided by a large number of agencies. Each event with magnitude triggers an automatic request for near real-time data at several national and international data centres. Moment tensor inversion is performed using complete regional long-period (50–100 s) waveforms. Initially the data are inverted for a fixed depth to remove traces with a low signal-to-noise ratio. The remaining data are then inverted for several trial depths to find the best-fitting depth. Solutions are produced within 90 min of an earthquake. We analyse the results for the period 2000 April to 2002 April to evaluate the performance of the procedure. For quality assessment, we compared the results with the independent Swiss regional moment tensor catalogue (SRMT), and divided the 87 moment tensor solutions into three groups: 38 A-quality solutions with well-resolved , depth and focal mechanism; 21 B-quality solutions with well-resolved ; and 28 unreliable C-quality solutions. The non-homogeneous station and event distributions, varying noise level, and inaccurate earthquake locations affected solution quality. For larger events we consistently obtained A-quality solutions. For we obtained A- and B-quality solutions. Solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated. [ABSTRACT FROM AUTHOR]

Using a random effects model that takes into consideration the correlation of data recorded by a single seismic event, a database consisting of 195 recordings from 17 recent events is employed to develop empirical attenuation relationships for the geometric mean of horizontal peak ground acceleration and 5-percent damped spectral acceleration (Sa). The recordings employed are obtained from strong motion stations operating in Northwestern Turkey and resulted from events that include the Kocaeli (Mw=7.4) and the Du¨zce (Mw=7.1) earthquakes and their aftershocks as well as other events. By studying differences in standard errors, the random effects model is compared with a fixed effects model that does not account for distinctions between intra- and inter-event variability. Effects of local site conditions are included in the empirical relationships developed. The dependence on frequency of the various model parameters is also studied. Frequency-dependent attenuation coefficients for the proposed random effects models developed are summarized in tables to facilitate their use. [Copyright &y& Elsevier]

Most methods for assessment of in situ seismic soil liquefaction potential require evaluation of the earthquake-induced cyclic shear stress ratio (CSR). Estimates of the in situ CSR can be developed directly, using dynamic response analyses, but it is common in ‘simplified’ analysis methods to develop estimates of the in situ CSR using empirical relationships. Unfortunately, the most widely used existing empirical relationships are based on limited response analyses and do not take full advantage of current knowledge of factors affecting this response problem. As a result, they are both biased and unnecessarily imprecise. This paper presents the results of a relatively comprehensive suite of site response studies (2153 site response analyses), performed using carefully selected suites of site conditions and input time histories, to provide an improved basis for development of estimates of in situ CSR using the rd-approach. The resulting empirical correlations, developed using the Bayesian updating method, provide a much improved basis for simplified empirical evaluation of CSR as a function of (1) depth; (2) earthquake magnitude; (3) intensity of shaking; and (4) site stiffness. [Copyright &y& Elsevier]

An endeavor is made to compute peak ground horizontal accelerations at bedrock level in the Delhi region due to the seismogenic sources present around Delhi. The entire area is divided into six seismogenic sources for which seismic hazard analysis is carried out using the complete and extreme part of the seismicity data. Maximum likelihood estimates of hazard parameters viz., seismic activity rate λ, b value and maximum probable earthquake Mmax are made for each zone. The return periods and the probabilities of occurrence of various magnitudes for return periods of 50, 100 and 1000 years are also computed for each zone. The peak ground acceleration (PGA) values for 20% exceedance in 50 years are then computed for the Delhi region from each zone. The maximum PGA value considering all the zones is 0.34 g, which is due to the Mathura fault zone. The seismogenic zones V and VI, i.e., Mathura fault zone and the Sohna fault zone are observed to be contributing maximum PGA values in the Delhi region governing the isoacceleration contours computed for the region. The seismic zonation map for the PGA values at the bedrock level is obtained for the Delhi region. This can be used directly as input for the microzonation of ground motion at the surface by incorporating the local site conditions. [ABSTRACT FROM AUTHOR]

The Aftershock sequence of Chamoli earthquake (Mw 6.4) of 29 March 1999 is analyzed to study the fractal structure in space, time and magnitude distribution. The b value is found to be 0.63 less than which is usually observed worldwide and in the Himalayas. This indicates that the numbers of smaller earthquakes are relatively less than the larger ones. The spatial correlation is 1.64, indicating that events are approaching a two-dimensional region meaning that the aftershocks are uniformly distributed along the trend of the aftershock zone. Temporal correlation is 0.86 for aftershocks of M ≥ 1, indicating a nearly continuous aftershock activity. However, it is 0.5 for aftershocks of M ≥ 1.75, indicating a non continuous aftershock activity. From the assessment of slip on different faults it is inferred that 70% displacement is accommodated on the primary fault and the remainder on secondary faults. [ABSTRACT FROM AUTHOR]

In aseismic regions the lack of large earthquakes in modern times makes the study of historical earthquakes essential as such events often serve as the yardstick for estimating seismic hazards. Since the largest earthquakes with few exceptions took place hundreds of years ago we may claim that their recurrence times are very large or alternatively their magnitudes are biased upwards. Scandinavia is no exception in this regard and one interesting event in particular is the Kattegat earthquake of 22 December 1759. It is unique in the sense that a macroseismic questionnaire was circulated in Zealand within days of its occurrence. The puzzling feature here is that intensity ranges from VII to I across Zealand but then given I=III for Hamburg and other North German cities. We have chosen two avenues in reassessing the magnitude of the Kattegat earthquake, namely (1) 2D finite-difference (FD) waveform modelling to evaluate possible amplitude amplifications due to sub-surface basin structures and (2) re-assessing the intensity reports of the 1759 Kattegat earthquake in light of the new European Macroseismic Scale (EMS-98).Our 2D FD results show that the presence of the Danish and the North German basins led to shear wave amplitude amplification by factors of 10 and 5, respectively. This is equivalent to a significant increase or overestimation of the area of perception (tied to I=III). The re-assessment of the macroseismic observations in light of the above results and the EMS-98 downgrade the Kattegat earthquake MS magnitude from 5.6 to 5.1. [Copyright &y& Elsevier]

Presents the Israel Seismic Network to partially distribute multichannel system for discrimination of low-magnitude event. Analysis of underwater explosions in terms of spectrum; Use of conventional single-station methods based on different spectral features; Development of multistation based on frequency spectral modulation method.

The article focuses on the two earthquakes that occurred in the northeastern Indian Ocean on April 11, 2012 with a magnitude of 8.6 and 8.2. It says that the earthquakes will mark in the annals of seismology due to its unusual high magnitudes, unexpected event in the strike-slip faulting mechanism, and the complexity of the rupture for intervening plate. It mentions that the event has shown the failure of oceanic lithosphere.

On 14 February 2006, an earthquake of magnitude 5.3 struck to the west of Phodong, a small town in the Himalayan State of Sikkim. The earthquake was followed by a large number of aftershocks that were recorded by a network of digital seismic stations operated by the National Geophysical Research Institute, Hyderabad. The study indicates an east-west trend of the epicentral distribution of earthquakes, which is correlated with the decollement plane of the Main Boundary Thrust dipping northward in Sikkim Himalaya. The Sikkim region is surrounded by several damaging earthquakes of the past, although it has not experienced a magnitude 8.0 earthquake so far. However, it remains to be seen whether the Sikkim region is a potentially less hazardous zone or there is likelihood of occurrence of a great earthquake in the near future. [ABSTRACT FROM AUTHOR]

We showed that the rupture produced by the great Peru earthquake (moment magnitude 8.4) on 23 june 2001 propagated for ∼70 kilometers before encountering a 6000-square-kilometer area of fault that acted as a barrier. The rupture continued around this barrier, which remained unbroken for ∼30 seconds and then began to break when the main rupture front was ∼200 kilometers from the epicenter. The barrier had relatively low rupture speed, slip, and aftershock density as compared to its surroundings, and the time of the main energy release in the earthquake coincided with the barrier's rupture. We associate this barrier with a fracture zone feature on the subducting oceanic plate. [ABSTRACT FROM AUTHOR]

Reports on the extensive study of earthquakes around the Pacific Rim suggesting the possibility of predicting the final size of an earthquake. Start of the onset of earthquakes; Dependence of the final magnitude of an earthquake on what happens in its first few seconds; Lack of difference between the beginning of a large earthquake and the beginning of a small earthquake.