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In this study, we estimate the location and magnitude of Central Asian earthquake from macroseismic intensity data. A set of 2373 intensity observations from 15 earthquakes is analysed to calibrate non-parametric models for the source and attenuation with distance, the distance being computed from the instrumental epicentres located according to the International Seismological Centre (ISC) catalogue. In a second step, the non-parametric source model is regressed against different magnitude values (e.g. MLH, mb, MS, Mw) as listed in various instrumental catalogues. The reliability of the calibrated model is then assessed by applying the methodology to macroseismic intensity data from 29 validation earthquakes for which both MLH and mb are available from the Central Asian Seismic Risk Initiative (CASRI) project and the ISC catalogue. An overall agreement is found for both the location and magnitude of these events, with the distribution of the differences between instrumental and intensity-based magnitudes having almost a zero mean, and standard deviations equal to 0.30 and 0.44 for mb and MLH, respectively. The largest discrepancies are observed for the location of the 1985, MLH = 7.0 southern Xinjiang earthquake, whose location is outside the area covered by the intensity assignments, and for the magnitude of the 1974, mb = 6.2 Markansu earthquake, which shows a difference in magnitude greater than one unit in terms of MLH. Finally, the relationships calibrated for the non-parametric source model are applied to assign different magnitude-scale values to earthquakes that lack instrumental information. In particular, an intensity-based moment magnitude is assigned to all of the validation earthquakes. [ABSTRACT FROM AUTHOR]

A temporary seismic network composed of 11 stations was installed in the city of Potenza (Southern Italy) to record local and regional seismicity within the context of a national project funded by the Italian Department of Civil Protection (DPC). Some stations were moved after a certain time in order to increase the number of measurement points, leading to a total of 14 sites within the city by the end of the experiment. Recordings from 26 local earthquakes (M 2.2−3.8 ) were analyzed to compute the site responses at the 14 sites by applying both reference and non-reference site techniques. Furthermore, the Spectral Intensity (SI) for each local earthquake, as well as their ratios with respect to the values obtained at a reference site, were also calculated. In addition, a field survey of 233 single station noise measurements within the city was carried out to increase the information available at localities different from the 14 monitoring sites. By using the results of the correlation analysis between the horizontal-to-vertical spectral ratios computed from noise recordings (NHV) at the 14 selected sites and those derived by the single station noise measurements within the town as a proxy, the spectral intensity correction factors for site amplification obtained from earthquake analysis were extended to the entire city area. This procedure allowed us to provide a microzonation map of the urban area that can be directly used when calculating risk scenarios for civil defence purposes. The amplification factors estimated following this approach show values increasing along the main valley toward east where the detrital and alluvial complexes reach their maximum thickness. [ABSTRACT FROM AUTHOR]

SUMMARY Simulations of strong ground motion within the Santiago de Chile Metropolitan area were carried out by means of 3-D deterministic wave propagation tool based on the spectral element method. The simulated events take into account the pronounced interface between the low-velocity sedimentary basin and the bedrock as well as topography of the area. To verify our model we simulated a regional earthquake recorded by a dense network installed in the city of Santiago for recording aftershock activity after the 2010 February 27 Maule main shock. The results proof the alluvial basin amplification effects and show a strong dependence of spectral amplification in the basin on the local site conditions. Moreover, we studied the seismic response due to a hypothetical Mw= 6.0 event occurring along the active San Ramón Fault, which is crossing the eastern edge of the city. The scenario earthquakes exhibit that an unfavourable interaction between fault rupture, radiation mechanism and complex geological and topographic conditions in the near-field region may give rise to large values of peak ground velocity in the basin. Finally, 3-D numerical predictions of ground motion are compared with the one computed according to ground motion prediction equations selected among the next generation attenuation relationships, in terms of ground motion peak values and spectral acceleration. The comparison underlines that the 3-D scenario simulations predict a significantly higher level of ground motion in the Santiago basin, especially over deep alluvial deposits. Moreover, also the location of the rupture nucleation largely influences the observed shaking pattern. [ABSTRACT FROM AUTHOR]

A seismic antenna approach based on the generalized zero-lag cross-correlation method for rapid earthquake localization is proposed. This method is intended to be applied primarily for early warning, whenever the epicentre-to-target distances guarantee enough lead-time, rapid response purposes, and for those circumstances when a seismogenic area is not directly accessible with seismic stations or/and a network of instruments is concentrated within the area to be warned. The procedure we propose aims to provide useful information for magnitude determination and shake-maps generation. Indeed, it relies only on the first P-wave triggered arrivals from seismic stations, and is designed to work in real-time for the localization of events occurring outside of the network, that is, under conditions that might be detrimental to standard localization approaches. The procedure can by summarized by a few preliminary pre-seismic and real-time co-seismic steps. In the pre-seismic time-frame, for the cases where a large and dense network exists, waiting for all stations to trigger could dramatically reduce the available lead-time for the warning. Therefore, in such cases, the network could profitably be divided into sub-arrays, while also taking advantage of available earthquake recordings or simulated data sets. During the co-seismic time-frame, the main operations are: (1) individual on-site triggering by the P-wave of the seismic stations (e.g. by a STA/LTA algorithm); (2) real-time communication of key parameters (e.g. P-wave arrival time, and signal quality) to a main centre by SMS/WLAN; (3) setup of a pseudo data set, composed by a Gaussian function centred at the P-time, and with a bell width that can be set up proportional to the trigger signal-to-noise ratio (SNR); (4) calculation of a coherency map for the sub-array with triggered stations (preliminary sub-array location); and (5) stacking of coherency maps from the different sub-arrays (final location). By the stack of coherency maps estimated by the different sub-arrays in the last step of the procedure, the epicentral area's location may be better constrained. This innovative approach for rapid localization was applied to both synthetic data, and real observations of two small earthquakes that occurred in the Marmara Sea, Turkey, which were recorded by the Istanbul Earthquake Rapid Response System. [ABSTRACT FROM AUTHOR]

We determined a high-resolution 3-D S-wave velocity model for a 26 km × 12 km area in the northern part of the basin of Santiago de Chile. To reach this goal, we used microtremor recordings at 125 sites for deriving the horizontal-to-vertical (H/V) spectral ratios that we inverted to retrieve local S-wave velocity profiles. In the inversion procedure, we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements, which were found to vary substantially over short distances in the investigated area. The resulting model was derived by interpolation with a kriging technique between the single S-wave velocity profiles and shows locally good agreement with the few existing velocity profile data, but allows the entire area, as well as deeper parts of the basin, to be represented in greater detail. The wealth of available data allowed us to check if any correlation between the S-wave velocity in the uppermost 30 m ( ) and the slope of topography, a new technique recently proposed by Wald and Allen, exists on a local scale. We observed that while one lithology might provide a greater scatter in the velocity values for the investigated area, almost no correlation between topographic gradient and calculated exists, whereas a better link is found between and the local geology. Finally, we compared the distribution with the MSK intensities for the 1985 Valparaiso event, pointing out that high intensities are found where the expected values are low and over a thick sedimentary cover. Although this evidence cannot be generalized for all possible earthquakes, it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the Santiago basin. [ABSTRACT FROM AUTHOR]

Over the last few years, the analysis of seismic noise recorded by two dimensional arrays has been confirmed to be capable of deriving the subsoil shear-wave velocity structure down to several hundred meters depth. In fact, using just a few minutes of seismic noise recordings and combining this with the well known horizontal-to-vertical method, it has also been shown that it is possible to investigate the average one dimensional velocity structure below an array of stations in urban areas with a sufficient resolution to depths that would be prohibitive with active source array surveys, while in addition reducing the number of boreholes required to be drilled for site-effect analysis. However, the high cost of standard seismological instrumentation limits the number of sensors generally available for two-dimensional array measurements (i.e., of the order of 10), limiting the resolution in the estimated shear-wave velocity profiles. Therefore, new themes in site-effect estimation research by two-dimensional arrays involve the development and application of low-cost instrumentation, which potentially allows the performance of dense-array measurements, and the development of dedicated signal-analysis procedures for rapid and robust estimation of shear-wave velocity profiles. In this work, we present novel low-cost wireless instrumentation for dense two-dimensional ambient seismic noise array measurements that allows the real-time analysis of the surface-wavefield and the rapid estimation of the local shear-wave velocity structure for site response studies. We first introduce the general philosophy of the new system, as well as the hardware and software that forms the novel instrument, which we have tested in laboratory and field studies. [ABSTRACT FROM AUTHOR]

It is common practice in the seismological community to use, especially for large earthquakes, the moment magnitude Mw as a unique magnitude parameter to evaluate the earthquake's damage potential. However, as a static measure of earthquake size, Mw does not provide direct information about the released seismic wave energy and its high frequency content, which is the more interesting information both for engineering purposes and for a rapid assessment of the earthquake's shaking potential. Therefore, we recommend to provide to disaster management organizations besides Mw also sufficiently accurate energy magnitude determinations as soon as possible after large earthquakes. We developed and extensively tested a rapid method for calculating the energy magnitude Me within about 10–15 min after an earthquake's occurrence. The method is based on pre-calculated spectral amplitude decay functions obtained from numerical simulations of Green's functions. After empirical validation, the procedure has been applied offline to a large data set of 767 shallow earthquakes that have been grouped according to their type of mechanism (strike-slip, normal faulting, thrust faulting, etc.). The suitability of the proposed approach is discussed by comparing our rapid Me estimates with Mw published by GCMT as well as with Mw and Me reported by the USGS. Mw is on average slightly larger than our Me for all types of mechanisms. No clear dependence on source mechanism is observed for our Me estimates. In contrast, Me from the USGS is generally larger than Mw for strike-slip earthquakes and generally smaller for the other source types. For ∼67 per cent of the event data set our Me differs ≤±0.3 magnitude units (m.u.) from the respective Me values published by the USGS. However, larger discrepancies (up to 0.8 m.u.) may occur for strike-slip events. A reason of that may be the overcorrection of the energy flux applied by the USGS for this type of earthquakes. We follow the original definition of magnitude scales, which does not apply a priori mechanism corrections to measured amplitudes, also since reliable fault-plane solutions are hardly available within 10–15 min after the earthquake origin time. Notable is that our uncorrected Me data show a better linear correlation and less scatter with respect to Mw than Me of the USGS. Finally, by analysing the recordings of representative recent pairs of strong and great earthquakes, we emphasize the importance of combining Mw and Me in the rapid characterization of the seismic source. They are related to different aspects of the source and may differ occasionally even more than 1 m.u. This highlights the usefulness and importance of providing these two magnitude estimates together for a better assessment of an earthquake's shaking potential and/or tsunamigenic potential. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss various reports within the special on topics including earthquake early warning (EEW), operational earthquake forecasting, and real-time structural monitoring.

Situated in an active tectonic region, Santiago de Chile, the country's capital with more than six million inhabitants, faces tremendous earthquake risk. Macroseismic data for the 1985 Valparaiso event show large variations in the distribution of damage to buildings within short distances, indicating strong effects of local sediments on ground motion. Therefore, a temporary seismic network was installed in the urban area for recording earthquake activity and a study was carried out aiming to estimate site amplification derived from horizontal-to-vertical ( H/ V) spectral ratios from earthquake data (EHV) and ambient noise (NHV), as well as using the standard spectral ratio (SSR) technique with a nearby reference station located on igneous rock. The results lead to the following conclusions: (1) The analysis of earthquake data shows significant dependence on the local geological structure with respect to amplitude and duration. (2) An amplification of ground motion at frequencies higher than the fundamental one can be found. This amplification would not be found when looking at NHV ratios alone. (3) The analysis of NHV spectral ratios shows that they can only provide a lower bound in amplitude for site amplification. (4) P-wave site responses always show lower amplitudes than those derived by S waves, and sometimes even fail to provide some frequencies of amplification. (5) No variability in terms of time and amplitude is observed in the analysis of the H/ V ratio of noise. (6) Due to the geological conditions in some parts of the investigated area, the fundamental resonance frequency of a site is difficult to estimate following standard criteria proposed by the SESAME consortium, suggesting that these are too restrictive under certain circumstances. [ABSTRACT FROM AUTHOR]

The Pisco earthquake ( Mw 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 1021 Nm ( Mw 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687. [ABSTRACT FROM AUTHOR]

Significant land subsidence was recently recognized in northeast Iran, near the city of Mashhad. Precise levelling surveys performed in 1995, 2002 and 2005, indicate as much as 90 cm of subsidence during the 1995–2005 period. Continuous GPS monitoring approximately 8 km northwest of Mashhad City shows more than 20 cm yr−1 subsidence between 2005 and 2006. We use Interferometric Synthetic Aperture Radar (InSAR) measurements to detect the temporal and spatial pattern of this surface deformation. 13 interferograms from 10 C-band SAR images acquired by the Enivsat satellite from 2003 to 2005 are analysed and stacked. Our InSAR mapping suggests that subsidence occurs within a northwest–southeast elongated elliptic-shaped bowl along the axis of the Mashhad valley, with a peak amplitude of for the 2003–2005 time period. The InSAR data indicate that approximately 70 km2 in the valley floor, including the northwestern part of Mashhad City, subsided at a rate exceeding 15 cm yr−1 between 2003 and 2005, and that the subsidence area is structurally controlled by the trends of Quaternary faults cutting the valley floor. Analysis of piezometric records suggests that subsidence likely results from extensive overdrafting of the aquifer system in the valley that has caused as much as 65 m of water table decline since 1960s. [ABSTRACT FROM AUTHOR]

We used new precise leveling data acquired 40 days after the Bam earthquake in combination with radar interferometry observations from both ascending and descending orbits to investigate static deformation associated with the 2003 Bam earthquake. We invert this geodetic data set to gain insight into the fault geometry and slip distribution of the rupture. The best-fitting dislocation model is a steeply east-dipping right-lateral strike-slip fault that has a size of 11 by 8 km and strikes N2°W. We find that such smooth geometry fits available geodetic data better than previously proposed models for this earthquake. Our distributed slip model indicates a maximum strike slip of 3 m occurring about 3 to 5 km deep. The slip magnitude and depth of faulting taper to the north, where the fault approaches the Bam city. Inclusion of crustal layering increases the amount of maximum slip inferred at depth by about 4%. [ABSTRACT FROM AUTHOR]

By analysing several years of discharge and electrical conductivity data from an artesian well in Kajaran, Armenia, we found a significant sensitivity of this well to distant large earthquakes. In general, the discharge increases co-seismically and the conductivity decreases post-seismically with a time delay of about 1 hr. The post-seismic trends of the conductivity reach a minimum after about 3 weeks and then need several months to recover to the pre-seismic level. For instance, the Izmit earthquake in Turkey on 1999 August 17, at a distance of 1400 km, led to an increase of 25 per cent in discharge and a decrease of up to 6 per cent in conductivity. The discharge also shows tidal fluctuations of amplitude roughly 5 per cent (peak-to-peak) of the mean well production, whereas the tidal signal in the conductivity data is less significant and unstable. The maximum co-seismic static strain estimated for 11 earthquakes that induced an anomaly during the monitoring period is below 10−9, or at least one order smaller than the tidal strain. Therefore, the well-water anomalies related to the distant earthquakes are believed to be induced by seismic ground shaking rather than co-seismic deformation. We suggest mixing of groundwater as an explanation for the observations and present a model which considers specific conditions for this particular groundwater system: a confined aquifer with a high contrast in the hydrogeochemical composition between two different groundwaters and a macrofracture as the mixing zone which is hydraulically connected to the artesian well. The earthquake-related anomalies are believed to result from a local head increase near the artesian well, induced by the passage of seismic waves. Possible mechanisms are discussed, and the time histories of the anomalies are modelled. [ABSTRACT FROM AUTHOR]

Analyzes the surface rupture of the Izmit earthquake of August 17, 1999. Fault traces; Crustal deformations; Maximum surface slop; Tectonic deformation.