TY - JOUR A1 - Ktenidou, Olga-Joan A1 - Roumelioti, Zafeiria A1 - Abrahamson, Norman A1 - Cotton, Fabrice A1 - Pitilakis, Kyriazis A1 - Hollender, Fabrice T1 - Understanding single-station ground motion variability and uncertainty (sigma) BT - lessons learnt from EUROSEISTEST JF - Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering N2 - Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30–50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φ S2S (20–30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9–90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φ SS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φ SS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φ SS , provided that: (1) the magnitude scaling errors are accommodated by the event terms; (2) there are no distance scaling errors (use of a regionally applicable model). Site terms (φ S2S ) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e., for hard rock. KW - Ground motion KW - Variability KW - Uncertainty KW - Single station sigma KW - Site response Y1 - 2018 U6 - https://doi.org/10.1007/s10518-017-0098-6 SN - 1570-761X SN - 1573-1456 VL - 16 IS - 6 SP - 2311 EP - 2336 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Bommer, Julian J. A1 - Scherbaum, Frank A1 - Bungum, Hilmar A1 - Cotton, Fabrice A1 - Sabetta, F. A1 - Abrahamson, Norman A. T1 - On the use of logic trees for ground-motion prediction equations in seismic-hazard analysis N2 - Logic trees are widely used in probabilistic seismic hazard analysis as a tool to capture the epistemic uncertainty associated with the seismogenic sources and the ground-motion prediction models used in estimating the hazard. Combining two or more ground-motion relations within a logic tree will generally require several conversions to be made, because there are several definitions available for both the predicted ground-motion parameters and the explanatory parameters within the predictive ground-motion relations. Procedures for making conversions for each of these factors are presented, using a suite of predictive equations in current use for illustration. The sensitivity of the resulting ground-motion models to these conversions is shown to be pronounced for some of the parameters, especially the measure of source-to-site distance, highlighting the need to take into account any incompatibilities among the selected equations. Procedures are also presented for assigning weights to the branches in the ground-motion section of the logic tree in a transparent fashion, considering both intrinsic merits of the individual equations and their degree of applicability to the particular application Y1 - 2005 SN - 0037-1106 ER - TY - JOUR A1 - Zali, Zahra A1 - Ohrnberger, Matthias A1 - Scherbaum, Frank A1 - Cotton, Fabrice A1 - Eibl, Eva P. S. T1 - Volcanic tremor extraction and earthquake detection using music information retrieval algorithms JF - Seismological research letters N2 - Volcanic tremor signals are usually observed before or during volcanic eruptions and must be monitored to evaluate the volcanic activity. A challenge in studying seismic signals of volcanic origin is the coexistence of transient signal swarms and long-lasting volcanic tremor signals. Separating transient events from volcanic tremors can, therefore, contrib-ute to improving upon our understanding of the underlying physical processes. Exploiting the idea of harmonic-percussive separation in musical signal processing, we develop a method to extract the harmonic volcanic tremor signals and to detect tran-sient events from seismic recordings. Based on the similarity properties of spectrogram frames in the time-frequency domain, we decompose the signal into two separate spec-trograms representing repeating (harmonic) and nonrepeating (transient) patterns, which correspond to volcanic tremor signals and earthquake signals, respectively. We reconstruct the harmonic tremor signal in the time domain from the complex spectrogram of the repeating pattern by only considering the phase components for the frequency range in which the tremor amplitude spectrum is significantly contribut-ing to the energy of the signal. The reconstructed signal is, therefore, clean tremor signal without transient events. Furthermore, we derive a characteristic function suitable for the detection of tran-sient events (e.g., earthquakes) by integrating amplitudes of the nonrepeating spectro-gram over frequency at each time frame. Considering transient events like earthquakes, 78% of the events are detected for signal-to-noise ratio = 0.1 in our semisynthetic tests. In addition, we compared the number of detected earthquakes using our method for one month of continuous data recorded during the Holuhraun 2014-2015 eruption in Iceland with the bulletin presented in Agustsdottir et al. (2019). Our single station event detection algorithm identified 84% of the bulletin events. Moreover, we detected a total of 12,619 events, which is more than twice the number of the bulletin events. KW - algorithms KW - body waves KW - earthquakes KW - elastic waves KW - eruptions KW - geologic hazards KW - natural hazards KW - P-waves KW - S-waves KW - seismic waves KW - signal-to-noise ratio KW - swarms KW - volcanic earthquakes Y1 - 2021 U6 - https://doi.org/10.1785/0220210016 SN - 0895-0695 SN - 1938-2057 VL - 92 IS - 6 SP - 3668 EP - 3681 PB - Seismological Society of America CY - Boulder, Colo. ER - TY - JOUR A1 - Zhu, Chuanbin A1 - Cotton, Fabrice A1 - Kawase, Hiroshi A1 - Händel, Annabel A1 - Pilz, Marco A1 - Nakano, Kenichi T1 - How well can we predict earthquake site response so far? BT - site-specific approaches JF - Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute N2 - Earthquake site responses or site effects are the modifications of surface geology to seismic waves. How well can we predict the site effects (average over many earthquakes) at individual sites so far? To address this question, we tested and compared the effectiveness of different estimation techniques in predicting the outcrop Fourier site responses separated using the general inversion technique (GIT) from recordings. Techniques being evaluated are (a) the empirical correction to the horizontal-to-vertical spectral ratio of earthquakes (c-HVSR), (b) one-dimensional ground response analysis (GRA), and (c) the square-root-impedance (SRI) method (also called the quarter-wavelength approach). Our results show that c-HVSR can capture significantly more site-specific features in site responses than both GRA and SRI in the aggregate, especially at relatively high frequencies. c-HVSR achieves a "good match" in spectral shape at similar to 80%-90% of 145 testing sites, whereas GRA and SRI fail at most sites. GRA and SRI results have a high level of parametric and/or modeling errors which can be constrained, to some extent, by collecting on-site recordings. KW - Site response KW - site effects KW - HVSR KW - ground response analysis KW - square-root-impedance KW - earthquake Y1 - 2022 U6 - https://doi.org/10.1177/87552930211060859 SN - 8755-2930 SN - 1944-8201 VL - 38 IS - 2 SP - 1047 EP - 1075 PB - Sage Publ. CY - Thousand Oaks ER - TY - JOUR A1 - Kotha, Sreeram Reddy A1 - Cotton, Fabrice A1 - Bindi, Dino T1 - A new approach to site classification BT - Mixed-effects Ground Motion Prediction Equation with spectral clustering of site amplification functions JF - Soil Dynamics and Earthquake Engineering N2 - With increasing amount of strong motion data, Ground Motion Prediction Equation (GMPE) developers are able to quantify empirical site amplification functions (delta S2S(s)) from GMPE residuals, for use in site-specific Probabilistic Seismic Hazard Assessment. In this study, we first derive a GMPE for 5% damped Pseudo Spectral Acceleration (g) of Active Shallow Crustal earthquakes in Japan with 3.4 <= M-w <= 7.3 and 0 <= R-JB <= 600km. Using k-mean spectral clustering technique, we then classify our estimated delta S2S(s)(T = 0.01 - 2s) of 588 wellcharacterized sites, into 8 site clusters with distinct mean site amplification functions, and within-cluster site-tosite variability similar to 50% smaller than the overall dataset variability (phi(S2S)). Following an evaluation of existing schemes, we propose a revised data-driven site classification characterized by kernel density distributions of V-s30, V-s10, H-800, and predominant period (T-G) of the site clusters. KW - Mixed-effects regression KW - Ground Motion Prediction Equation KW - Site classification KW - Spectral clustering analysis KW - Empirical site amplification functions Y1 - 2018 U6 - https://doi.org/10.1016/j.soildyn.2018.01.051 SN - 0267-7261 SN - 1879-341X VL - 110 SP - 318 EP - 329 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - von Specht, Sebastian A1 - Heidbach, Oliver A1 - Cotton, Fabrice A1 - Zang, Arno T1 - Uncertainty reduction of stress tensor inversion with data-driven catalogue selection JF - Geophysical journal international N2 - The selection of earthquake focal mechanisms (FMs) for stress tensor inversion (STI) is commonly done on a spatial basis, that is, hypocentres. However, this selection approach may include data that are undesired, for example, by mixing events that are caused by different stress tensors when for the STI a single stress tensor is assumed. Due to the significant increase of FM data in the past decades, objective data-driven data selection is feasible, allowing more refined FM catalogues that avoid these issues and provide data weights for the STI routines. We present the application of angular classification with expectation-maximization (ACE) as a tool for data selection. ACE identifies clusters of FM without a priori information. The identified clusters can be used for the classification of the style-of-faulting and as weights of the FM data. We demonstrate that ACE effectively selects data that can be associated with a single stress tensor. Two application examples are given for weighted STI from South America. We use the resulting clusters and weights as a priori information for an STI for these regions and show that uncertainties of the stress tensor estimates are reduced significantly. KW - Inverse Theory KW - Statistical Methods KW - Seismicity KW - tectonics KW - Kinematics of crustal KW - mantle deformation Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy240 SN - 0956-540X SN - 1365-246X VL - 214 IS - 3 SP - 2250 EP - 2263 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Letort, Jean A1 - Retailleau, Lise A1 - Boue, Pierre A1 - Radiguet, Mathilde A1 - Gardonio, Blandine A1 - Cotton, Fabrice A1 - Campillo, Michel T1 - Lateral variations of the Guerrero-Oaxaca subduction zone (Mexico) derived from weak seismicity (M(b)3.5+) detected on a single array at teleseismic distance JF - Geophysical journal international N2 - Detections of pP and sP phase arrivals (the so-called depth phases) at teleseismic distance provide one of the best ways to estimate earthquake focal depth, as the P-pP and the P-sP delays are strongly dependent on the depth. Based on a new processing workflow and using a single seismic array at teleseismic distance, we can estimate the depth of clusters of small events down to magnitude M-b 3.5. Our method provides a direct view of the relative variations of the seismicity depth from an active area. This study focuses on the application of this new methodology to study the lateral variations of the Guerrero subduction zone (Mexico) using the Eielson seismic array in Alaska (USA). After denoising the signals, 1232 M-b 3.5 + events were detected, with clear P, pP, sP and PcP arrivals. A high-resolution view of the lateral variations of the depth of the seismicity of the Guerero-Oaxaca area is thus obtained. The seismicity is shown to be mainly clustered along the interface, coherently following the geometry of the plate as constrained by the receiver-function analysis along the Meso America Subduction Experiment profile. From this study, the hypothesis of tears on the western part of Guerrero and the eastern part of Oaxaca are strongly confirmed by dramatic lateral changes in the depth of the earthquake clusters. The presence of these two tears might explain the observed lateral variations in seismicity, which is correlated with the boundaries of the slow slip events. KW - North America KW - Time-series analysis KW - Body waves KW - Earthquake source observations KW - Seismicity and tectonics Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy035 SN - 0956-540X SN - 1365-246X VL - 213 IS - 2 SP - 1002 EP - 1012 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Socquet, Anne A1 - Valdes, Jesus Pina A1 - Jara, Jorge A1 - Cotton, Fabrice A1 - Walpersdorf, Andrea A1 - Cotte, Nathalie A1 - von Specht, Sebastian A1 - Ortega-Culaciati, Francisco A1 - Carrizo, Daniel A1 - Norabuena, Edmundo T1 - An 8month slow slip event triggers progressive nucleation of the 2014 Chile megathrust JF - Geophysical research letters N2 - The mechanisms leading to large earthquakes are poorly understood and documented. Here we characterize the long-term precursory phase of the 1 April 2014 M(w)8.1 North Chile megathrust. We show that a group of coastal GPS stations accelerated westward 8months before the main shock, corresponding to a M(w)6.5 slow slip event on the subduction interface, 80% of which was aseismic. Concurrent interface foreshocks underwent a diminution of their radiation at high frequency, as shown by the temporal evolution of Fourier spectra and residuals with respect to ground motions predicted by recent subduction models. Such ground motions change suggests that in response to the slow sliding of the subduction interface, seismic ruptures are progressively becoming smoother and/or slower. The gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the main shock. KW - seismology KW - GPS KW - subduction KW - precursor Y1 - 2017 U6 - https://doi.org/10.1002/2017GL073023 SN - 0094-8276 SN - 1944-8007 VL - 44 SP - 4046 EP - 4053 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Kotha, Sreeram Reddy A1 - Weatherill, Graeme A1 - Bindi, Dino A1 - Cotton, Fabrice T1 - Near-source magnitude scaling of spectral accelerations BT - analysis and update of Kotha et al. (2020) model JF - Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering N2 - Ground-motion models (GMMs) are often used to predict the random distribution of Spectral accelerations (SAs) at a site due to a nearby earthquake. In probabilistic seismic hazard and risk assessment, large earthquakes occurring close to a site are considered as critical scenarios. GMMs are expected to predict realistic SAs with low within-model uncertainty (sigma(mu)) for such rare scenarios. However, the datasets used to regress GMMs are usually deficient of data from critical scenarios. The (Kotha et al., A Regionally Adaptable Ground-Motion Model for Shallow Crustal Earthquakes in Europe Bulletin of Earthquake Engineering 18:4091-4125, 2020) GMM developed from the Engineering strong motion (ESM) dataset was found to predict decreasing short-period SAs with increasing M-W >= M-h = 6.2, and with large sigma(mu) at near-source distances <= 30km. In this study, we updated the parametrisation of the GMM based on analyses of ESM and the Near source strong motion (NESS) datasets. With M-h = 5.7, we could rectify the M-W scaling issue, while also reducing sigma(mu). at M-W >= M-h. We then evaluated the GMM against NESS data, and found that the SAs from a few large, thrust-faulting events in California, New Zealand, Japan, and Mexico are significantly higher than GMM median predictions. However, recordings from these events were mostly made on soft-soil geology, and contain anisotropic pulse-like effects. A more thorough non-ergodic treatment of NESS was not possible because most sites sampled unique events in very diverse tectonic environments. We provide an updated set of GMM coefficients,sigma(mu), and heteroscedastic variance models; while also cautioning against its application for M-W <= 4 in low-moderate seismicity regions without evaluating the homogeneity of M-W estimates between pan-European ESM and regional datasets. KW - Ground-motion model KW - Spectral accelerations KW - Magnitude scalin KW - Near-source saturation KW - Within-model uncertainty KW - Heteroscedastic KW - variability Y1 - 2022 U6 - https://doi.org/10.1007/s10518-021-01308-5 SN - 1570-761X SN - 1573-1456 VL - 20 IS - 3 SP - 1343 EP - 1370 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Delavaud, Elise A1 - Cotton, Fabrice A1 - Akkar, Sinan A1 - Scherbaum, Frank A1 - Danciu, Laurentiu A1 - Beauval, Celine A1 - Drouet, Stephane A1 - Douglas, John A1 - Basili, Roberto A1 - Sandikkaya, M. Abdullah A1 - Segou, Margaret A1 - Faccioli, Ezio A1 - Theodoulidis, Nikos T1 - Toward a ground-motion logic tree for probabilistic seismic hazard assessment in Europe JF - Journal of seismology N2 - The Seismic Hazard Harmonization in Europe (SHARE) project, which began in June 2009, aims at establishing new standards for probabilistic seismic hazard assessment in the Euro-Mediterranean region. In this context, a logic tree for ground-motion prediction in Europe has been constructed. Ground-motion prediction equations (GMPEs) and weights have been determined so that the logic tree captures epistemic uncertainty in ground-motion prediction for six different tectonic regimes in Europe. Here we present the strategy that we adopted to build such a logic tree. This strategy has the particularity of combining two complementary and independent approaches: expert judgment and data testing. A set of six experts was asked to weight pre-selected GMPEs while the ability of these GMPEs to predict available data was evaluated with the method of Scherbaum et al. (Bull Seismol Soc Am 99:3234-3247, 2009). Results of both approaches were taken into account to commonly select the smallest set of GMPEs to capture the uncertainty in ground-motion prediction in Europe. For stable continental regions, two models, both from eastern North America, have been selected for shields, and three GMPEs from active shallow crustal regions have been added for continental crust. For subduction zones, four models, all non-European, have been chosen. Finally, for active shallow crustal regions, we selected four models, each of them from a different host region but only two of them were kept for long periods. In most cases, a common agreement has been also reached for the weights. In case of divergence, a sensitivity analysis of the weights on the seismic hazard has been conducted, showing that once the GMPEs have been selected, the associated set of weights has a smaller influence on the hazard. KW - Logic trees KW - Ground-motion prediction equations KW - Expert judgment KW - Model selection KW - Seismic hazard assessment Y1 - 2012 U6 - https://doi.org/10.1007/s10950-012-9281-z SN - 1383-4649 VL - 16 IS - 3 SP - 451 EP - 473 PB - Springer CY - Dordrecht ER -