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For simulating the dynamic rupture process in earthquake scenarios, the stress distribution along the fault remains unclear owing to a lack of direct measurements. Regional stress fields are often resolved onto the fault plane to determine the stress distribution along it. To overcome this limitation, we considered different interseismic locking models to better constrain the actual stress distribution. Specifically, we took the Suoerkuli section in the middle of the Altyn Tagh fault, China, and conducted dynamic rupture simulations to obtain possible earthquake scenarios. The surface rupture length and moment magnitude obtained from the simulations were consistent with those of historical earthquakes. Compared with the traditional stress field resolution method, our approach led to better constrained fault rupture extent and distribution characteristics of regional intensity, thereby avoiding overestimations of earthquake damage. We conclude that examining regional seismic hazards and risks based on seismic dynamic rupture simulations that account for the locking ratio of the fault plane is advantageous, and should be encouraged. [ABSTRACT FROM AUTHOR]

To provide timely and accurate seismic alerts for potential users during the earthquake early warning (EEW) process, several algorithms have been proposed and implemented. Some of the most common rely on the characterization of the earthquake magnitude and location, and then use a ground motion model to forecast shaking intensity at a user's location. It has been noted that with this approach the scatter in the forecasted intensities can be significant and may affect the reliability and usefulness of the warnings. To ameliorate this, we propose a single station machine learning (ML) algorithm. We build a four-layer convolutional neural network (CNN), named it CONIP (Convolutional neural network ONsite Intensity Prediction), and test it using two data sets to study the feasibility of seismic intensity forecasting from only the first few seconds of a waveform. With only limited waveforms, mainly P waves, our CONIP model will forecast the on-site seismic intensity. We find that compared with existing methods, the forecasted seismic intensities are much more accurate. To understand the nature of this improvement we carry out a residual decomposition and quantify to what degree the ML model learns site, regional path, and source information during the training. We find that source and site effects are easily learned by the algorithm. Path effects, on the other hand, can be learned but will depend largely on the number, location, and coverage of stations. Overall, the ML model performance is a substantial improvement over traditional approaches. Our results are currently only applicable for small and moderate intensities but, we argue, could in future work be supplemented by simulations to supplement the training data sets at higher intensities. We believe that ML algorithms will play a dominant role in the next generation of EEW systems. [ABSTRACT FROM AUTHOR]

SUMMARY: We derived new, reversible relationships between macroseismic intensity (I), expressed in either the European Macroseismic (EMS-98) or the Mercalli–Cancani–Sieberg (MCS) scales and peak ground acceleration (PGA), peak ground velocity (PGV) and the spectral acceleration (SA) at 0.3, 1.0 and 3.0 s [SA(0.3), SA(1.0) and SA(3.0)] for Italy. We adopted the orthogonal distance regression technique to fit a quadratic function. This research aims to improve ground motion and intensity estimates for earthquake hazard applications, and for the calculation of shakemaps in Italy. To this end, the recently published INGe data set was used (https://doi.org/10.13127/inge.2). The new relations are: where PGA and SAs are expressed in cm s−2 and PGV is expressed in cm s−1. Tests performed to assess the robustness and the accuracy of the results demonstrate that adoption of quadratic relationships for this regression problem is a suitable choice within the range of values of the available data set. Comparison with similar published regressions for Italy evidences that the proposed relations provide statistically significant improved fits to the data. The new relations are also tested by inserting them in the ShakeMap system of the Italian configuration evidencing a significant improvement when compared to those implemented. [ABSTRACT FROM AUTHOR]

The ∼ M 6 1799 Bouin earthquake is considered as one of the largest earthquakes to have struck Western France. However, the seismogenic source potentially responsible for this event remain marginally documented. We present results from a focused offshore-onshore multidisciplinary survey in its meizoseismal area in order to identify the fault segments that potentially ruptured during this earthquake. Based on macroseismic data and the geology, we focused our study on the so-called Machecoul Fault as a potential source of the 1799 Bouin event. Our survey includes extensive high-resolution seismic reflection, high resolution bathymetry and a 1-yr seismological survey. These data were combined with existing topography, onshore gravity data and drill data to document the geometry of the Marais Breton/Baie de Bourgneuf basin, the past tectonic activity and the current local microearthquakes at depth along its bounding faults. Offshore and onshore observations suggest a recent activity of the segmented Machecoul Fault bounding the basin to the North. Offshore, the planar contact between the Plio-Quaternary sediments and the basement along the fault trace as well as the thickening of these sedimentary units near this contact suggests tectonic control rather than erosion. Onshore, the recent incision of the footwall of the fault suggests a recent tectonic activity. The temporary local seismological experiment deployed between 2016 and 2017 recorded a diffuse microseismicity down to the depth of 22 ± 5 km along the southward dipping Machecoul Fault, associated with predominantly normal fault mechanisms. Altogether, these results suggest that the Machecoul Fault is a serious candidate for being the source of the historical Bouin 1799 earthquake. [ABSTRACT FROM AUTHOR]

The spatial correlation of earthquake ground motion intensity can be measured from strong motion data; however, the data used in past studies is sparsely sampled in space, and only the interstation distance was considered as a correlation variable. These limitations mean that we have only weak constraints on the true correlation structure of ground motion and that potentially important aspects of spatial correlation are unconstrained. In this study, we combine a large-N seismic array and graph analytics to explore this issue at a local scale using small local and regional earthquakes. Our result suggests site conditions, and how they interact with the incident seismic wavefield, strongly condition the spatial correlation of ground motion. Future progress in characterizing ground motion spatial variability will require dense wavefield measurements, either through nodal deployments, or perhaps distributed acoustic sensing measurements, of seismic wavefields. Aftershock sequences of major earthquakes would provide particularly data-rich targets of opportunity. [ABSTRACT FROM AUTHOR]

On 24 August 2016 at 01:36 UTC a M L6.0 earthquake struck several villages in central Italy, among which Accumoli, Amatrice and Arquata del Tronto. The earthquake was recorded by about 350 seismic stations, causing 299 fatalities and damage with macroseismic intensities up to 11. The maximum acceleration was observed at Amatrice station (AMT) reaching 916 cm s–2 on E–W component, with epicentral distance of 15 km and Joyner and Boore distance to the fault surface (R JB) of less than a kilometre. Motivated by the high levels of observed ground motion and damage, we generate broad-band seismograms for engineering purposes by adopting a hybrid method. To infer the low frequency seismograms, we considered the kinematic slip model by Tinti et al. The high frequency seismograms were produced using a stochastic finite-fault model approach based on dynamic corner-frequency. Broad-band synthetic time-series were therefore obtained by merging the low and high frequency seismograms. Simulated hybrid ground motions were compared both with the observed ground motions and the ground-motion prediction equations (GMPEs), to explore their performance and to retrieve the region-specific parameters endorsed for the simulations. In the near-fault area we observed that hybrid simulations have a higher capability to detect near source effects and to reproduce the source complexity than the use of GMPEs. Indeed, the general good consistency found between synthetic and observed ground motion (both in the time and frequency domain), suggests that the use of regional-specific source scaling and attenuation parameters together with the source complexity in hybrid simulations improves ground motion estimations. To include the site effect in stochastic simulations at selected stations, we tested the use of amplification curves derived from HVRSs (horizontal-to-vertical response spectra) and from HVSRs (horizontal-to-vertical spectral ratios) rather than the use of generic curves according to NTC18 Italian seismic design code. We generally found a further reduction of residuals between observed and simulated both in terms of time histories and spectra. [ABSTRACT FROM AUTHOR]

Considering spatial correlation of multiple earthquake intensity measures (IMs) is of particular importance in loss assessment of spatially distributed assets. This subject has been investigated in previous studies under the assumption of isotropy. Considering the fact that the assumption of isotropy is not valid in general, the present study employs a non-separable covariance model based on latent dimensions method to investigate anisotropic properties of spatial correlations and cross-correlations of intra-event residuals of multiple earthquake IMs. This method leads to the generation of valid covariance matrix in order to model anisotropic spatially distributed multivariate random fields. Two sets of IMs are considered in this study; the first set consists of peak ground intensity values (acceleration, velocity, and displacement), and the second set consists of spectral accelerations at three different periods. Data of 10 earthquake events in California and Japan are utilized in this study to estimate parameters of marginal and cross-covariance models. Moreover, parameters of covariance model of regional site condition, which is considered as average shear wave velocity of top 30 m of soil profile (Vs30), are obtained in order to investigate the effect of local sited conditions on spatial correlations of IMs. It is shown that maximum range and anisotropy ratio of covariance models of intra-event residuals of IMs are correlated with those of Vs30 values. Also, it is observed that the anisotropy direction of residuals of IMs is consistent with anisotropy direction of Vs30 values. Finally, predictive models are proposed to obtain marginal and cross-covariance functions for different earthquake IMs considering anisotropy. [ABSTRACT FROM AUTHOR]

Due to complex 3-D heterogeneous structures, conventional 1-D analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3-D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough between April 2004 and August 2019 to evaluate decade-scale seismicity. Green's functions for CMT inversions of earthquakes with moment magnitudes of 4.3–6.5 were evaluated using finite-difference method simulations of seismic wave propagation in the regional 3-D velocity structure model. Significant differences of focal mechanisms and centroid depths between previous 1-D and our 3-D catalogues were found in the solutions of offshore earthquakes. By introducing the 3-D structures of the low-velocity accretionary prism and the Philippine Sea Plate, dip angles and centroid depths for offshore earthquakes were well-constrained. Teleseismic CMT also provides robust solutions, but our regional 3-D CMT could provide better constraints of dip angles. Our 3-D CMT catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the Nankai Trough. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths along the Nankai Trough plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution, regions with strong coupling were clearly identified. [ABSTRACT FROM AUTHOR]

This study describes a deep convolutional neural network (CNN) based technique to predict intensity measurements (IMs) of earthquake ground shaking. The input data to the CNN model consists of multistation, 3C acceleration waveforms recorded during the 2016 Central Italy earthquake sequence for M  ≥ 3.0 events. Using a 10 s window starting at the earthquake origin time, we find that the CNN is capable of accurately predicting IMs at stations far from the epicentre which have not yet recorded the maximum ground shaking. The CNN IM predictions do not require previous knowledge of the earthquake source (location and magnitude). Comparison between the CNN model predictions and those obtained with the Bindi et al. GMPE (which requires location and magnitude) shows that the CNN model features similar error variance but smaller bias. Although the technique is not strictly designed for earthquake early warning, we find that it can provide useful estimates of ground motions within 15–20 s after earthquake origin time depending on various setup elements (e.g. times for data transmission, computation, latencies). The technique has been tested on raw data without any initial data pre-selection in order to closely replicate real-time data streaming. When noise examples were included with the earthquake data the CNN was found to be stable, accurately predicting the ground shaking intensity corresponding to the noise amplitude. [ABSTRACT FROM AUTHOR]

We simulate 0–2.5 Hz deterministic wave propagation in 3-D velocity models for the 2008 Chino Hills, CA, earthquake using a finite-fault source model and frequency-dependent anelastic attenuation. Small-scale heterogeneities are modeled as 3-D random fields defined using an elliptically anisotropic von Kármán autocorrelation function with its parameters constrained using Los Angeles basin borehole data. We superimpose the heterogeneity models on a leading deterministic community velocity model (CVM) of southern California. We find that models of velocity and density perturbations can have significant effects on the wavefield at frequencies as low as 0.5 Hz, with ensemble median values of various ground motion metrics varying up to ±50 per cent compared to those computed using the deterministic CVM only. In addition, we show that frequency-independent values of the shear-wave quality factor (Q s0) parametrized as Q s0 = 150 Vs (Vs in km s–1) provides the best agreement with data when assuming the published moment magnitude (M w) of 5.4 (M 0 = 1.6 × 1017 Nm) for the finite-fault source model. This model for Q s0 trades off with Q s0 = 100 Vs assuming M w = 5.5 (M 0 = 2.2 × 1017 Nm), which represents an upper bound of the M w estimates for this event. We find the addition of small-scale heterogeneities provides limited overall improvement to the misfit between simulations and data for the considered ground motion metrics, because the primary sources of misfit originate from the deterministic CVM and/or the finite-fault source description. [ABSTRACT FROM AUTHOR]

This paper proposes a novel approach to the joint inversion of gravity and magnetic data based on multinary transformation of the model parameters and Gramian constraints. The concept of multinary transformation is a generalization of the binary density inversion for models described by any number of discrete model parameters, while the Gramian constraint enforces the linear relationships between the different model parameters and their attributes or transforms. By combining these two concepts, the joint multinary inversion using Gramian constraints not only makes it possible to explicitly exploit the sharp contrasts of the density and magnetic susceptibility between the host media and anomalous targets in the inversion of gravity and magnetic data, but also provides uniform spatial boundaries of the anomalous targets in the distributions of density and magnetic susceptibility. The novel joint multinary inversion algorithm is demonstrated to be effective in determining the shapes, locations and physical properties of the anomalous targets. We show that this method can be effectively applied to the joint inversion of the full tensor gravity gradiometry data and the total magnetic intensity data, computer simulated for 3-D synthetic models using ternary model transformation. We also tested this joint inversion algorithm in the area of the McFaulds Lake in northwestern Ontario, Canada, and the joint inversion results provide a reasonable geological model with high resolution for the exploration of magmatic chromite deposits. [ABSTRACT FROM AUTHOR]

To account for the randomness (aleatory variability) and limited knowledge (epistemic uncertainty) of earthquake processes, we must formulate and test seismic hazard models using the concepts of probability. Probabilistic seismic hazard analysis (PSHA) gives the chance that a specified seismic intensity will be exceeded at a particular site during some future time window. Because knowledge of that chance is uncertain, a complete PSHA estimate of probabilities must itself be expressed as a probability distribution, often quantified using expert opinion. The conceptual objections to PSHA stem primarily from the unsatisfactory treatment of the aleatory-epistemic duality in probabilistic inference and questions regarding the inherent testability of subjective models. We have proposed an augmented probabilistic framework that resolves these issues by adding a third level of uncertainty, which we term 'ontological error' (PNAS, 111, 11973, 2014). A complete probabilistic model is sufficient to pose an ontological null hypothesis, which states that the aleatory representation of future earthquake activity—the seismic behaviour of the real Earth—samples the probability distribution of aleatory representations that describe the model's epistemic uncertainty. We can test, and possibly reject, the ontological null hypothesis by employing an 'experimental concept' that identifies collections of data, observed and not yet observed, judged to be exchangeable (i.e. with joint probability distributions invariant to data ordering) when conditioned on a set of explanatory variables. These conditional exchangeability judgments specify data sequences with well-defined frequencies. Bayesian models that predict such long-run frequencies can thus be tested for ontological error by frequentist methods, for example using P -values. We describe examples of experimental concepts pertinent to the ontological testing of complete probabilistic earthquake forecasting models. The examples, which include both simple and compound exceedance testing, illustrate how test distributions can be derived from the de Finetti representation and its generalizations, the use of hierarchical statistical models to express the various layers of aleatory variability, and the importance of the 'Principle of Complete Ignorance' in characterizing ontological errors. We also show how differing experimental concepts can probe different model features and explore how experimental concepts can themselves be tested. [ABSTRACT FROM AUTHOR]

A high-resolution model of 3-D P -wave velocity (Vp) tomography of the crust in the source area of the 2016 Kumamoto earthquake (M 7.3) in West Japan is determined using a large number of arrival times of first P waves and reflected P waves from the Moho discontinuity (PmP). The PmP data are collected from original seismograms of the Kumamoto aftershocks and other local crustal events in Kyushu. Detailed resolution tests show that the addition of the PmP data can significantly improve the resolution of the crustal tomography, especially that of the lower crust. Our results show that significant low-velocity (low-V) anomalies exist in the entire crust beneath the active volcanoes, which may reflect the pathway of arc magma. The 2016 Kumamoto earthquake occurred at the edge of a small low-V zone in the upper crust. A significant low-V anomaly is revealed in the lower crust beneath the source zone, which may reflect the arc magma and fluids ascending from the mantle wedge. These results suggest that the rupture nucleation of the 2016 Kumamoto earthquake was affected by fluids and arc magma. [ABSTRACT FROM AUTHOR]

Macroseismic intensity is assessed on the basis of the effects caused by an earthquake. These effects reflect the expression of both the intensity and frequency of the ground motion, thus complicating prediction equation modelling. Here we analysed data of several macroseismic transitory effects caused by recent Italian earthquakes in order to study their attenuation as a function of magnitude and hypocentral distance and to obtain a specific prediction equation, of simple functional form, that could be applied to each of the effects under analysis. We found that the different attenuation behaviours could be clearly defined by the values of the specially formulated magnitude-distance scaling ratio (S), thus allowing to group the effects on the basis of the S value. The oscillation of hanging objects and liquids, together with the feeling of dizziness, were separated from most other variables, such as the effects of the earthquake on small objects, china and windows, which were caused by a vibration of higher frequency. Besides, the greater value of S, associated with the perception of the seismic sound, explained the peculiarity of this phenomenon. As a result, we recognized the frequency range associated with each effect through comparisons with the ground motion prediction equations and, in particular, with the 5 per cent damped horizontal response spectra. Here we show the importance of appropriately selecting the diagnostic elements to be used for intensity assessment in order to improve the correlation with ground motion. [ABSTRACT FROM AUTHOR]

The 2014 April 1, Mw 8.1 Iquique (Chile) earthquake struck in the Northern Chile seismic gap. With a rupture length of less than 200 km, it left unbroken large segments of the former gap. Early studies were able to model the main rupture features but results are ambiguous with respect to the role of aseismic slip and left open questions on the remaining hazard at the Northern Chile gap. A striking observation of the 2014 earthquake has been its extensive preparation phase, with more than 1300 events with magnitude above ML 3, occurring during the 15 months preceding the main shock. Increasing seismicity rates and observed peak magnitudes accompanied the last three weeks before the main shock. Thanks to the large data sets of regional recordings, we assess the precursor activity, compare foreshocks and aftershocks and model rupture preparation and rupture effects. To tackle inversion challenges for moderate events with an asymmetric network geometry, we use full waveforms techniques to locate events, map the seismicity rate and derive source parameters, obtaining moment tensors for more than 300 events (magnitudes Mw 4.0-8.1) in the period 2013 January 1-2014 April 30. This unique data set of fore- and aftershocks is investigated to distinguish rupture process models and models of strain and stress rotation during an earthquake. Results indicate that the spatial distributions of foreshocks delineated the shallower part of the rupture areas of the main shock and its largest aftershock, well matching the spatial extension of the aftershocks cloud. Most moment tensors correspond to almost pure double couple thrust mechanisms, consistent with the slab orientation. Whereas no significant differences are observed among thrust mechanisms in different areas, nor among thrust foreshocks and aftershocks, the early aftershock sequence is characterized by the presence of normal fault mechanisms, striking parallel to the trench but dipping westward. These events likely occurred in the shallow wedge structure close to the slab interface and are consequence of the increased extensional stress in this region after the largest events. The overall stress inversion result suggests a minor stress rotation after the main shock, but a significant release of the deviatoric stress. The temporal change in the distribution of focal mechanisms can also be explained in terms of the spatial heterogeneity of the stress field: under such interpretation, the potential of a large megathrust earthquake breaking a larger segment offshore Northern Chile remains high. [ABSTRACT FROM AUTHOR]

We recorded acoustic, seismic and radio-frequency signatures of 70 solid charge (~2-12 kg) surface explosions (shots) at local distances (0.1-1.5 km) to determine if such signals could be fused for blast monitoring. We observed that each geophysical signature was sufficiently repeatable between similar shots to be identifiable with multichannel correlation detectors. Using template signals from a large explosion, we then processed heavily contaminated data recording a smaller shot with these detectors, and missed or marginally detected the resultant target signals. By then fusing the p-values of these statistics through Fisher's combined probability test, we clearly identified the same explosion signals at thresholds consistent with the false alarm on noise rates of the correlation detectors. This resulting Fisher test thereby provided high-probability detections, zero false alarms and higher theoretical detection capability. [ABSTRACT FROM AUTHOR]

We present new archaeointensity results from three Italian kilns situated at Ascoli Satriano, Vagnari and Fontanetto Po obtained with the Thellier modified by Coe double heating method. These data complement the directional results previously published. All sites are dated on the basis of archaeological information and/or thermoluminescence dating. The results are corrected for the anisotropy of the thermoremanent magnetization and the cooling rate effects. The new data are compared with previously published archaeointensity data from Italy and nearby countries within 900 km radius from Viterbo. An initial data set including archaeointesity data mainly coming from Italy, France, Switzerland, Czech Republic, Slovakia, Hungary, Greece and Bulgaria has been compiled. After the application of strict selection criteria, the most reliable data have been used for the calculation of a preliminary Italian intensity secular variation (SV) curve for the last 3000 yr. The new curve covers the 300 BC–400 AD and 1200–1900 AD periods. It is established by means of sliding windows of 200 yr shifted by 100 yr. The lack of reliable data for the 1000–200 BC and 400–1200 AD time intervals does not permit the calculation of a continuous curve. Clearly, more high-quality archaeointensity data from Italy and Europe are still needed to draw a robust intensity SV curve for the Italian Peninsula that could be used for archaeomagnetic dating in combination with the directional data. [ABSTRACT FROM AUTHOR]

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]

New experimental and computational approaches to interpret orientation and intensity of natural remanent magnetization (NRM) carried by lamellar magnetism are applied to historic magnetic measurements on a collection of 82 massive hemo-ilmenite samples from the Allard Lake District in the Grenville Province, Quebec. The anisotropy of magnetic susceptibility (AMS), together with declination and inclination of NRM, indicate a systematic deflection β of the NRM vector away from the unit vector v that represents the Mesoproterozoic magnetizing field direction. The deflection β is caused by a statistical lattice-preferred orientation (LPO) of the individual (0001) basal planes, to which the NRM is confined in hemo-ilmenite crystals. Here, we study a second deflection ψ that is the angle the NRM makes with the statistical (0001) basal plane of the crystal assemblage, in relation to the angle α between the statistical (0001) basal plane and v. The relation between these two angles depends on the scatter of the distribution of crystal platelets, which also influences the AMS of the assemblage. For a Fisher distribution of basal planes, the distribution parameter K can be determined from ψ and α. It is then further possible to infer the single-crystal anisotropy of individual platelets. Typical crystals of hemo-ilmenite turn out to have a relatively weak AMS so that samples with a narrow Fisher distribution of platelets nevertheless can have a weak AMS. This has been confirmed in two samples by measurement of the (0001) basal plane distribution of crystals using electron backscatter diffraction, and in one of these two samples by measuring AMS and NRM of a single hemo-ilmenite crystal. Based on our estimated K values for selected samples, we calculate values of β, NRM intensity and ψ for any value of α. These data provide striking examples of the influence of the orientation of the crystal LPO on the intensity of lamellar magnetism, and explain the large variation of observed NRM intensities by varying orientation with respect to the magnetizing field, without requiring large variations of the paleomagnetic field intensity. This relation between NRM and LPO is also important for anomaly interpretation in areas with strong foliation. [ABSTRACT FROM AUTHOR]

SUMMARY We analyse the spatial distribution of the intensity data points surveyed after the Mw 6.3, 2009 L'Aquila (central Italy) earthquake, with the aim to recognize and quantify finite-fault and directivity effects. The study is based on the analysis of the residuals, evaluated with respect to attenuation-with-distance models, calibrated for L'Aquila earthquake. We apply a non-parametric approach considering both the epicentral and the rupture distance, which accounts for the finite extension of the source. Then, starting from a simplified kinematic rupture model of the L'Aquila fault, we compute four directivity predictors proposed in literature, and assess their correlation with intensity residuals. We derive a so-called Intensity Directivity Factor by the correlation between theoretical predictors and observed residuals that allows us to identify and quantify the intensity data points affected by forward and backward directivity during L'Aquila earthquake. We find that the effects are more pronounced in the forward directivity direction and increments up to 1 MCS intensity unit are expected. Moreover, the directivity predictor that accounts for radiation pattern poorly correlates with residuals. These results show that the spatial distribution of the L'Aquila macroseismic field is affected by source effects and in particular that directivity-induced amplification effects can be recognized. We show that the quasi-unilateral rupture propagation along the fault can explain the high-intensity patterns observed along specific direction at relatively large distance from the instrumental epicentre, in accordance with the seismological source models derived from the analysis of instrumental observations. [ABSTRACT FROM AUTHOR]

Petrophysical, in particular seismic velocity, measurements of the Outokumpu deep drill core (depth 2.5 km) have been carried out to characterize the geophysical nature of the Paleoproterozoic crustal section of eastern Finland and to find lithological and geophysical interpretations to the distinct crustal reflectors as observed in seismic surveys. The results show that different lithological units can be identified based on the petrophysical data. The density of the samples remained nearly constant throughout the drilled section. Only diopside-tremolite skarns and black schists exhibit higher densities. The samples are dominated by the paramagnetic behaviour with occasional ferromagnetic signature caused by serpentinitic rocks. Large variations in seismic velocities, both at ambient pressure and under in situ crustal conditions are observed. The porosity of the samples, which is extremely low, is either intrinsic by nature or caused by decompaction related to fracturing during the core retrieval. It is noteworthy that these microfractures have dramatically lowered the V and V values. From the measured velocities and density data we have calculated the seismic impedances, Young's modulus and Poisson's ratios for the lithological units of the Outokumpu section and from these data the reflection coefficients for the major lithological boundaries, evident in the surveyed section, were determined. The data show that the strong and distinct reflections visible in wide-angle seismic surveys are caused by interfaces between diopside-tremolite skarn and either serpentinites, mica schist or black schist. [ABSTRACT FROM AUTHOR]

We study a large = 7.6 earthquake that occurred on 2007 November 14 in the Northern Chile seismic gap near the city of Tocopilla. Using a variety of seismic data we show that this earthquake ruptured only the lower part of the interplate seismic zone and generated a series of plate interface aftershocks. Two large aftershocks on 2007 November 15 ruptured the interplate zone oceanwards of the Mejillones Peninsula, a major geographical feature in the Antofagasta region. On 2007 December 16, a large = 6.8 aftershock, that occurred near the southern bottom of the fault plane of the main event, is shown to be a slab-push earthquake located inside the subducted Nazca Plate and triggered by along slab compression. Aftershocks of this event demonstrate that it occurred on an almost vertical fault. The Tocopilla earthquake took place just after the installation of a new seismological network by Chilean, German and French researchers. The accelerometric data combined with far field seismic data provide a quite complete and consistent view of the rupture process. The earthquake broke a long (130 km) and narrow (about 30–50 km) zone of the plate interface just above the transition zone. Using a non-linear kinematic inversion method, we determined that rupture occurred on two well-defined patches of roughly elliptical shape. We discuss the consequences of this event for models of gap filling earthquakes in Chile proposed in the 1970s. [ABSTRACT FROM AUTHOR]

We attempt at providing new insights about the earthquake behaviour in western Taiwan, based on a comparison between historical information and present-day instrumental records. We provide a consistent picture of the earthquake history during the last four centuries and draw some inferences in terms of seismic cycle. Before instrumental seismic observation in Taiwan started at the end of the 19th century, ancient written earthquake records are available from the ancient Chinese governments and the public concerning the 17th, 18th and 19th centuries. Distribution of casualties and property damage, indicating seismic intensity, can be estimated from archives. Using the Central Weather Bureau (CWB) intensity scale we calibrate the intensity–magnitude relationships from the instrumental seismicity recorded from 1995 to 2005, showing that within the range of historical uncertainties and earthquake depths in western Taiwan, 0–40 km, the depth is not critical in these relationships. With estimated intensities, the magnitudes of historical earthquakes can be evaluated based on a single average empirical relationship between ML, the local magnitude, and I0, the epicentral intensity: ML= 0.08 I02– 0.04 I0+ 3.41. Three types of diagrams are then proposed to describe the historical seismicity. The first type involves simple representation of earthquake events according to time and magnitude. The second type involves cumulative plot of the released elastic energy with time, as calculated from reconstructed magnitudes. The third type of diagram shows the evolution of cumulative seismic strain release with time, based on a Benioff's law indicating that the release of elastic strain related to an earthquake is proportional to the square root of the dissipated energy. These curves highlight inferences of historical seismicity analysis in terms of earthquake frequency and seismic cycle duration in the different segments of the front belt and foreland zones of western Taiwan, with large contrasts suggesting different levels in earthquake hazard. [ABSTRACT FROM AUTHOR]

We present an extension of the theory of the time-frequency (TF) misfit criteria for quantitative comparison of time signals. We define TF misfit criteria for quantification and characterization of disagreement between two three-component signals. We distinguish two cases—with and without having one signal as reference. We define locally and globally normalized TF criteria. The locally normalized misfits can be used if it is important to investigate relatively small parts of the signal (e.g. wave groups, pulses, transients, spikes, so-called seismic phases) no matter how large amplitudes of those parts are with respect to the maximum amplitude of the signal. They provide a detailed TF anatomy of the disagreement between two entire signals. The globally normalized misfits can be used for quantifying an overall level of disagreement. They allow accounting for both the envelope/phase difference at a TF point and the significance of the envelope at that point with respect to the maximum envelope of the signal. We also introduce the TF envelope and phase goodness-of-fit criteria based on the complete signal representation, and thus suitable for comparing arbitrary time signals in their entire TF complexity. The TF goodness-of-fit criteria quantify the level of agreement and are most suitable in the case of larger differences between the signals. We numerically demonstrate the capability and important features of the TF misfit and goodness-of-fit criteria in the methodologically important examples. [ABSTRACT FROM AUTHOR]

We present new data that explores the link between pore pressure and seismic velocity to estimate the magnitude of the overpressure within the deep sediments of the Eastern Black Sea basin. New wide-angle seismic data, combined with coincident reflection data, have been modelled simultaneously using the seismic tomography code, Jive3D, to provide a well-constrained seismic velocity model of the sediments. Our models reveal a widespread low-velocity zone at the depth of 5.5–8.5 km, which is characterized by a velocity decrease from 3.5 to ∼2.5 km s−1. Using two separate methods that relate changes in seismic velocity to changes in effective stress, we estimate pore pressures of at least 160 MPa within the low-velocity zone. These pore pressures give values of 0.8–0.9 within the centre of the basin and above the Mid-Black Sea High. The low-velocity zone occurs within the Maikop formation, an organic-rich mud layer identified as the source of mud volcanism in the Black Sea and South Caspian Sea. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the crustal and uppermost mantle structure beneath Toba caldera, which is known as the location of one of the largest Cenozoic eruptions on Earth. The most recent event occurred 74 000 yr BP, and had a significant global impact on climate and the biosphere. In this study, we revise data on local seismicity in the Toba area recorded by a temporary PASSCAL network in 1995. We applied the newest version of the LOTOS-07 algorithm, which includes absolute source location, optimization of the starting 1-D velocity model, and iterative tomographic inversion for 3-D seismic P, S (or the VP/ VS ratio) and source parameters. Special attention is paid to verification of the obtained results. Beneath the Toba caldera and other volcanoes of the arc, we observe relatively moderate (for volcanic areas) negative P- and S-velocity anomalies that reach 18 per cent in the uppermost layer, 10–12 per cent in the lower crust and about 7 per cent in the uppermost mantle. Much stronger contrasts are observed for the VP/ VS ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies. At a depth of 5 km beneath active volcanoes, we observe small patterns (7–15 km size) with a high VP/ VS ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes. In the mantle wedge, we observe a vertical anomaly with low P and S velocities and a high VP/ VS ratio that link the cluster of events at 120–140 km depth with Toba caldera. This may be an image of ascending fluids and melts released from the subducted slab due to phase transitions. However, taking into account poor vertical resolution, these results should be interpreted with prudence. Although the results show clear signatures that are quite typical for volcanic areas (low velocity and high VP/ VS ratio beneath volcanoes), we do not observe any specific features in seismic structure that could characterize Toba as a super volcano. [ABSTRACT FROM AUTHOR]

This is the second paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to use the velocity model that was proposed and validated in the companion paper for seismic intensity modelling of the 1969 ( Ms= 8.0) and 1755 ( M= 8.5–8.7) earthquakes. First, we propose a regression to convert simulated values of Peak Ground Velocity (PGV) into Modified Mercalli Intensity (MMI) in SW Iberia, and using this regression, we build synthetic isoseismal maps for a large ( Ms= 8.0) earthquake that occurred in 1969. Based on information on the seismic source provided by various authors, we show that the velocity model effectively reproduces macroseismic observations in the whole region. We also confirm that seismic intensity distribution is very sensitive to a small number of source parameters: rupture directivity, fault strike and fault dimensions. Then, we extrapolate the method to the case of the great ( M= 8.5–8.7) 1755 earthquake, for a series of hypotheses recently proposed by three authors about the location of the epicentral region. The model involving a subduction-related rupture in the Gulf of Cádiz results in excessive ground motion in northern Morocco, suggesting that the source of the 1755 earthquake should be located further west. A rupture along the western coast of Portugal, compatible with an activation of the passive western Iberian margin, would imply a relatively low average slip, which, alone, would could not account for the large tsunami observed in the whole northern Atlantic ocean. A seismic source located below the Gorringe Bank seems the most likely since it is more efficient in reproducing the distribution of high intensities in SW Iberia due to the 1755 earthquake. [ABSTRACT FROM AUTHOR]

We develop a method to obtain confidence intervals of earthquake source parameters, such as stress drop, seismic moment and corner frequency, from single station measurements. We use the idea of jackknife variance combined with a multitaper spectrum estimation to obtain the confidence regions. The approximately independent spectral estimates provide an ideal case to perform jackknife analysis. Given the particular properties of the problem to solve for source parameters, including high dynamic range, non-negativity, non-linearity, etc., a log transformation is necessary before performing the jackknife analysis. We use a Student's t distribution after transformation to obtain accurate confidence intervals. Even without the distribution assumption, we can generate typical standard deviation confidence regions. We apply this approach to four earthquakes recorded at 1.5 and 2.9 km depth at Cajon Pass, California. It is necessary to propagate the errors from all unknowns to obtain reliable confidence regions. From the example, it is shown that a 50 per cent error in stress drop is not unrealistic, and even higher errors are expected if velocity structure and location errors are present. An extension to multiple station measurement is discussed. [ABSTRACT FROM AUTHOR]

We have implemented surface wave full ray theory to investigate the influence of source, path and receiver effects on observed minor- and major-arc, long period , three-component surface waves. Calculations are carried out using a variety of global tomographic earth models. We conduct a synthetic numerical study of phase and amplitude anomalies due to source, path and receiver effects. We estimate that the influence of the local structure at the receiver is generally negligible compared with the other terms. Phase anomalies are mostly controlled by path effects. However, amplitude variations due to the source, particularly due to the local structure at the source, are also important. We show that, for the tomographic models we use, in theory this type of anomaly is as important as that produced by focusing and defocusing effects along the propagation path. We present results of a statistical experiment to assess the impact of these effects on the fit to observed waveforms. As expected, waveforms calculated using laterally varying models match the data better than spherical earth calculations. The improved waveform fit is mainly caused by more accurate phase predictions due to path corrections. On average, calculations using the laterally varying models do not improve the amplitude fit compared with that for a spherically symmetric earth. We assess the impact of uncertainties in the source mechanism and location on the anomalies, by updating the seismic source parameters using an inversion scheme similar to the Harvard CMT method. Even after correcting for the earthquake source location and mechanism, on average, the laterally varying tomographic models used in this study do not explain observed surface wave amplitudes better than spherical earth calculations. This probably reflects unmodelled effects, such as lateral variations in attenuation, azimuthal anisotropy and finite frequency effects. However, it also suggests that new earth models need to be built fully exploiting all the information in the data, particularly amplitudes. [ABSTRACT FROM AUTHOR]

Ambient vibration techniques such as the H/V method may have the potential to significantly contribute to site effect evaluation, particularly in urban areas. Previous studies interpret the so-called Nakamura's technique in relation to the ellipticity ratio of Rayleigh waves, which, for a high enough impedance contrast, exhibits a pronounced peak close to the fundamental S-wave resonance frequency. Within the European SESAME project (Site EffectS assessment using AMbient Excitations) this interpretation has been tested through noise numerical simulation under well-controlled conditions in terms of source type and distribution and propagation structure. We will present simulations for a simple realistic site (one sedimentary layer over bedrock) characterized by a rather high impedance contrast and low quality factor. Careful H/V and array analysis on these noise synthetics allow an in-depth investigation of the link between H/V ratio peaks and the noise wavefield composition for the soil model considered here: (1) when sources are near (4 to 50 times the layer thickness) and surficial, H/V curves exhibit one single peak, while the array analysis shows that the wavefield is dominated by Rayleigh waves; (2) when sources are distant (more than 50 times the layer thickness) and located inside the sedimentary layer, two peaks show up on the H/V curve, while the array analysis indicates both Rayleigh waves and strong S head waves; the first peak is due to both fundamental Rayleigh waves and resonance of head S waves, the second is only due to the resonance of head S waves; (3) when sources are deep (located inside the bedrock), whatever their distance, H/V ratio exhibit peaks at the fundamental and harmonic resonance frequencies, while array analyses indicate only non-dispersive body waves; the H/V is thus simply due to multiple reflections of S waves within the layer. Therefore, considering that experimental H/V ratio (i.e. derived from actual noise measured in the field) exhibit in most cases only one peak, we conclude that H/V ratio is (1) mainly controlled by local surface sources, (2) mainly due to the ellipticity of the fundamental Rayleigh waves. Then the amplitude of H/V peak is not able to give a good estimate of site amplification factor. [ABSTRACT FROM AUTHOR]

The microwave palaeointensity technique has been used to determine palaeointensity during the R3–N3 geomagnetic field reversal, using lavas from the Esja region of southwestern Iceland. The resulting intensity determinations have been compared to two previous studies which used the Shaw and Thellier techniques. Both reported low field intensities during the reversal except for four flows that produced high values (20.4–36.8 μT) using the Shaw technique compared to a single maximum intermediate value of 15.9 μT using the Thellier method. In this paper, an average microwave transitional palaeointensity of 6.95 ± 2.07 μT is found for samples used in the Shaw technique study, and of 7.80 ± 1.61 μT for samples used in the Thellier study, demonstrating that there is no evidence for strong fields during this reversal. [ABSTRACT FROM AUTHOR]

The Woodlark rift system is one of the few places where active ocean basin formation can be studied. Within this rift system, continental extension rates are some of the fastest on the planet, and extension progresses eastwards to full seafloor spreading. We use results from a recent passive seismic experiment to address the role of magmatism prior to the onset of seafloor spreading. We invert local earthquake P and S traveltimes for 3-D structure around and ahead of the active spreading tip. From the local earthquake tomography we observe three main structures. Seismic velocities in the crust show a sharp contrast between regions that resemble continental crust ahead of the spreading tip and oceanic crust to the east. In the continental portion, P velocities increase from 5.6 km s−1 to 6.9 km s−1 between 10 and 25 km depth, indicating a bulk felsic to intermediate composition, similar to other continental regions. Beneath the seismic Moho (23–28 km depth, as defined by receiver functions) a 10–15-km-thick gradient zone exist locally with velocities from 7.0 to 7.9 km s−1, which may reflect an underplated mafic, granulite facies lowermost crust, or perhaps magmatic intrusion into the lithospheric mantle. In contrast, farther east and closer to the active spreading tip, velocities rapidly increase from 6.5 to 7.2 km s−1 between 8 and 18 km depth. These fast crustal velocities appear in a narrow zone roughly 60 km wide and indicate a mafic crust, similar to oceanic crust. Our velocity results suggest that the transition from diffuse continental rifting to localized seafloor spreading likely occurs across a narrow zone. Magmatism prior to the onset of seafloor spreading may not play a significant role in altering crust until the onset of seafloor spreading, except through underplating at the base of the crust. [ABSTRACT FROM AUTHOR]

The 1855 earthquake at Visp remains the strongest in the last 300 yr in Switzerland. It caused heavy damage in the region of the middle Valais. We reconstructed the damage field of this event studying also site effects and building vulnerability. The key factors in such a study are the availability and accessibility of sufficient historical data. Given the existence of a complete contemporary damage assessment and the availability of early statistics, our investigation drew upon an excellent pool of data. These sources enabled us to quantitatively analyse the damage field on the village level. Other historical sources described some of the losses with more detail but not across the whole area. These data were qualitatively analysed and then used to calibrate and verify the outcomes of the quantitative analysis. When it was possible to describe the damage fields of single villages, as with Visp, a high percentage of damaged buildings could be located so exactly as to foster further investigation. In addition we identified several secondary effects such as rock fall, landslides and changes in the subsurface. The observed damages support the thesis of a normal fault striking along the Valley of Visp (north–south) and dipping to the west. [ABSTRACT FROM AUTHOR]

Finite-fault source inversions reveal the spatial complexity of earthquake slip or pre-stress distribution over the fault surface. The basic assumption of this study is that a stochastic model can reproduce the variability in amplitude and the long-range correlation of the spatial slip distribution. In this paper, we compute the stochastic model for the source models of four earthquakes: the 1979 Imperial Valley, the 1989 Loma Prieta, the 1994 Northridge and 1995 Hyogo-ken Nanbu (Kobe). For each earthquake (except Imperial Valley), we consider both the dip and strike slip distributions. In each case, we use a 1-D stochastic model. For the four earthquakes, we show that the average power spectra of the raw, that is, non-interpolated, data follow a power-law behaviour with scaling exponents that range from 0.78 to 1.71. For the four earthquakes, we have found that a non-Gaussian probability law, that is, the Lévy law, is better suited to reproduce the main features of the spatial variability embedded in the slip amplitude distribution, including the presence and frequency of large fluctuations. Since asperities are usually defined as regions with large slip values on the fault, the stochastic model will allow predicting and modelling the spatial distribution of the asperities over the fault surface. The values of the Lévy parameters differ from one earthquake to the other. Assuming an isotropic spatial distribution of heterogeneity for the dip and the strike slip of he Northridge earthquake, we also compute a 2-D stochastic model. The main conclusions reached in the 1-D analysis remain appropriate for the 2-D model. The results obtained for the four earthquakes suggest that some features of the slip spatial complexity are universal and can be modelled accordingly. If this is proven correct, this will imply that the spatial variability and the long-range correlation of the slip or pre-stress spatial distribution can be described with the help of five parameters: a scaling exponent controlling the spatial correlation and the four parameters of the Lévy distribution constraining the spatial variability. [ABSTRACT FROM AUTHOR]

Intensity assignments for 33 calibration earthquakes were used to develop intensity attenuation models for the Alps, Armorican, Provence, Pyrenees and Rhine regions of France. Intensity decreases with Δ most rapidly in the French Alps, Provence and Pyrenees regions, and least rapidly in the Armorican and Rhine regions. The comparable Armorican and Rhine region attenuation models are aggregated into a French stable continental region model and the comparable Provence and Pyrenees region models are aggregated into a Southern France model. We analyse MSK intensity assignments using the technique of Bakun & Wentworth, which provides an objective method for estimating epicentral location and intensity magnitude MI. MI for the 1356 October 18 earthquake in the French stable continental region is 6.6 for a location near Basle, Switzerland, and moment magnitude M is 5.9–7.2 at the 95 per cent (±2σ) confidence level. MI for the 1909 June 11 Trevaresse (Lambesc) earthquake near Marseilles in the Southern France region is 5.5, and M is 4.9–6.0 at the 95 per cent confidence level. Bootstrap resampling techniques are used to calculate objective, reproducible 67 per cent and 95 per cent confidence regions for the locations of historical earthquakes. These confidence regions for location provide an attractive alternative to the macroseismic epicentre and qualitative location uncertainties used heretofore. [ABSTRACT FROM AUTHOR]

We here describe one way of constructing internal multiples from surface seismic data only. The key feature of our construct of internal multiples is the introduction of the concept of virtual seismic events. Virtual events here are events, which are not directly recorded in standard seismic data acquisition, but their existence allows us to construct internal multiples with scattering points at the sea surface; the standard construct of internal multiples does not include any scattering points at the sea surface. The mathematical and computational operations invoked in our construction of virtual events and internal multiples are similar to those encountered in the construction of free-surface multiples based on the Kirchhoff or Born scattering theory. For instance, our construct operates on one temporal frequency at a time, just like free-surface demultiple algorithms; other internal multiple constructs tend to require all frequencies for the computation of an internal multiple at a given frequency. It does not require any knowledge of the subsurface nor an explicit knowledge of specific interfaces that are responsible for the generation of internal multiples in seismic data. However, our construct requires that the data be divided into two, three or four windows to avoid generating primaries. This segmentation of the data also allows us to select a range of periods of internal multiples that one wishes to construct because, in the context of the attenuation of internal multiples, it is important to avoid generating short-period internal multiples that may constructively average to form primaries at the seismic scale. [ABSTRACT FROM AUTHOR]

Discusses a hybrid technique to model the effect of topography on coseismic displacements. Coseismic deformations; Finite-element method; Elastic spaces.

Describes the radial receiver functions calculated from teleseisms recorded by broad-band seismometers distributed in Iceland. Factors influencing the arrival time of direct P phase on radial receiver functions; Increase of seismic velocities of the crust; Nature and depth of crust-mantle transition.

Part II. Assesses the accumulates melt beneath slow spreading ridge from wide-angle refraction and multichannel reflection seismic. Discussions on the process of crustal accretion; Evaluation on the forward modelling of seismic and gravity data; Observation on magma chambers beneath slow spreading ridges.

Examines the radiative transfer and diffusion of waves in layered medium. Discussions on the seismic coda in homologeneous media exhibiting discontinuity of physical properties; Effects on the contrast of wave velocities; Validity of diffusion approximation to provide analytical form for decay in the late coda.

Examines the three-dimensional geometrical ray theory and modelling of transmitted seismic energy data from the Nevada Test Site. Algorithm of synthetic seismogram computation for velocity distribution; Performance of 3-D ray tracing for traveltimes and geometrical spreading; Solution of the two-point ray-tracing problem by ray direction adjustments.

The article presents a list of forthcoming articles and reading sources on geophysics including "Linear Pressurization Method for Determining Hydraulic Permeability and Specific Storage of a Rock Sample," by I. Song and J. Renner, "Regional Intensity Attenuation Models for France and the Estimation of Magnitude and Localization of Historical Earthquakes," by W. H. Bakun and O. Scotti, and "Stress Interaction Between Seismic and Volcacnic Activity at Mt. Etna," by N. Feuillet, M. Cocco, C. Musumeci and C. Nostro.