TY - JOUR A1 - Weatherill, Graeme A1 - Cotton, Fabrice Pierre T1 - A ground motion logic tree for seismic hazard analysis in the stable cratonic region of Europe BT - regionalisation, model selection and development of a scaled backbone approach JF - Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering N2 - Regions of low seismicity present a particular challenge for probabilistic seismic hazard analysis when identifying suitable ground motion models (GMMs) and quantifying their epistemic uncertainty. The 2020 European Seismic Hazard Model adopts a scaled backbone approach to characterise this uncertainty for shallow seismicity in Europe, incorporating region-to-region source and attenuation variability based on European strong motion data. This approach, however, may not be suited to stable cratonic region of northeastern Europe (encompassing Finland, Sweden and the Baltic countries), where exploration of various global geophysical datasets reveals that its crustal properties are distinctly different from the rest of Europe, and are instead more closely represented by those of the Central and Eastern United States. Building upon the suite of models developed by the recent NGA East project, we construct a new scaled backbone ground motion model and calibrate its corresponding epistemic uncertainties. The resulting logic tree is shown to provide comparable hazard outcomes to the epistemic uncertainty modelling strategy adopted for the Eastern United States, despite the different approaches taken. Comparison with previous GMM selections for northeastern Europe, however, highlights key differences in short period accelerations resulting from new assumptions regarding the characteristics of the reference rock and its influence on site amplification. KW - ground motion models KW - stable craton KW - regionalisation KW - epistemic KW - uncertainty KW - Europe Y1 - 2020 U6 - https://doi.org/10.1007/s10518-020-00940-x SN - 1570-761X SN - 1573-1456 VL - 18 IS - 14 SP - 6119 EP - 6148 PB - Springer Science + Business Media B.V. CY - Dordrecht ER - TY - JOUR A1 - von Specht, Sebastian A1 - Cotton, Fabrice Pierre T1 - A link between machine learning and optimization in ground-motion model development BT - weighted mixed-effects regression with data-driven probabilistic earthquake classification JF - Bulletin of the Seismological Society of America N2 - The steady increase of ground-motion data not only allows new possibilities but also comes with new challenges in the development of ground-motion models (GMMs). Data classification techniques (e.g., cluster analysis) do not only produce deterministic classifications but also probabilistic classifications (e.g., probabilities for each datum to belong to a given class or cluster). One challenge is the integration of such continuous classification in regressions for GMM development such as the widely used mixed-effects model. We address this issue by introducing an extension of the mixed-effects model to incorporate data weighting. The parameter estimation of the mixed-effects model, that is, fixed-effects coefficients of the GMMs and the random-effects variances, are based on the weighted likelihood function, which also provides analytic uncertainty estimates. The data weighting permits for earthquake classification beyond the classical, expert-driven, binary classification based, for example, on event depth, distance to trench, style of faulting, and fault dip angle. We apply Angular Classification with Expectation-maximization, an algorithm to identify clusters of nodal planes from focal mechanisms to differentiate between, for example, interface- and intraslab-type events. Classification is continuous, that is, no event belongs completely to one class, which is taken into account in the ground-motion modeling. The theoretical framework described in this article allows for a fully automatic calibration of ground-motion models using large databases with automated classification and processing of earthquake and ground-motion data. As an example, we developed a GMM on the basis of the GMM by Montalva et al. (2017) with data from the strong-motion flat file of Bastias and Montalva (2016) with similar to 2400 records from 319 events in the Chilean subduction zone. Our GMM with the data-driven classification is comparable to the expert-classification-based model. Furthermore, the model shows temporal variations of the between-event residuals before and after large earthquakes in the region. Y1 - 2020 U6 - https://doi.org/10.1785/0120190133 SN - 0037-1106 SN - 1943-3573 VL - 110 IS - 6 SP - 2777 EP - 2800 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Kotha, Sreeram Reddy A1 - Cotton, Fabrice Pierre 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 - Yepes, Hugo A1 - Audin, Laurence A1 - Alvarado, Alexandra A1 - Beauval, Celine A1 - Aguilar, Jorge A1 - Font, Yvonne A1 - Cotton, Fabrice Pierre T1 - A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment JF - Tectonics N2 - A new view of Ecuador's complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis. This study focuses on two aspects of the plates' interaction at a continental scale: (a) age-related differences in rheology between Farallon and Nazca plates—marked by the Grijalva rifted margin and its inland projection—as they subduct underneath central Ecuador, and (b) the rapidly changing convergence obliquity resulting from the convex shape of the South American northwestern continental margin. Both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling. Intermediate-depth seismicity reveals a severe flexure in the Farallon slab as it dips and contorts at depth, originating the El Puyo seismic cluster. The two slabs position and geometry below continental Ecuador also correlate with surface expressions observable in the local and regional geology and tectonics. The interseismic coupling is weak and shallow south of the Grijalva rifted margin and increases northward, with a heterogeneous pattern locally associated to the Carnegie ridge subduction. High convergence obliquity is responsible for the North Andean Block northeastward movement along localized fault systems. The Cosanga and Pallatanga fault segments of the North Andean Block-South American boundary concentrate most of the seismic moment release in continental Ecuador. Other inner block faults located along the western border of the inter-Andean Depression also show a high rate of moderate-size earthquake production. Finally, a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme. Y1 - 2016 U6 - https://doi.org/10.1002/2015TC003941 SN - 0278-7407 SN - 1944-9194 VL - 35 SP - 1249 EP - 1279 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Aiken, John M. A1 - Aiken, Chastity A1 - Cotton, Fabrice Pierre T1 - A python library for teaching computation to seismology students JF - Seismological research letters N2 - Python is at the forefront of scientific computation for seismologists and therefore should be introduced to students interested in becoming seismologists. On its own, Python is open source and well designed with extensive libraries. However, Python code can also be executed, visualized, and communicated to others with "Jupyter Notebooks". Thus, Jupyter Notebooks are ideal for teaching students Python and scientific computation. In this article, we designed an openly available Python library and collection of Jupyter Notebooks based on defined scientific computation learning goals for seismology students. The Notebooks cover topics from an introduction to Python to organizing data, earthquake catalog statistics, linear regression, and making maps. Our Python library and collection of Jupyter Notebooks are meant to be used as course materials for an upper-division data analysis course in an Earth Science Department, and the materials were tested in a Probabilistic Seismic Hazard course. However, seismologists or anyone else who is interested in Python for data analysis and map making can use these materials. Y1 - 2018 U6 - https://doi.org/10.1785/0220170246 SN - 0895-0695 SN - 1938-2057 VL - 89 IS - 3 SP - 1165 EP - 1171 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Bayona Viveros, Jose Antonio A1 - von Specht, Sebastian A1 - Strader, Anne A1 - Hainzl, Sebastian A1 - Cotton, Fabrice Pierre A1 - Schorlemmer, Danijel T1 - A Regionalized Seismicity Model for Subduction Zones Based on Geodetic Strain Rates, Geomechanical Parameters, and Earthquake-Catalog Data JF - Bulletin of the Seismological Society of America N2 - The Seismic Hazard Inferred from Tectonics based on the Global Strain Rate Map (SHIFT_GSRM) earthquake forecast was designed to provide high-resolution estimates of global shallow seismicity to be used in seismic hazard assessment. This model combines geodetic strain rates with global earthquake parameters to characterize long-term rates of seismic moment and earthquake activity. Although SHIFT_GSRM properly computes seismicity rates in seismically active continental regions, it underestimates earthquake rates in subduction zones by an average factor of approximately 3. We present a complementary method to SHIFT_GSRM to more accurately forecast earthquake rates in 37 subduction segments, based on the conservation of moment principle and the use of regional interface seismicity parameters, such as subduction dip angles, corner magnitudes, and coupled seismogenic thicknesses. In seven progressive steps, we find that SHIFT_GSRM earthquake-rate underpredictions are mainly due to the utilization of a global probability function of seismic moment release that poorly captures the great variability among subduction megathrust interfaces. Retrospective test results show that the forecast is consistent with the observations during the 1 January 1977 to 31 December 2014 period. Moreover, successful pseudoprospective evaluations for the 1 January 2015 to 31 December 2018 period demonstrate the power of the regionalized earthquake model to properly estimate subduction-zone seismicity. Y1 - 2019 U6 - https://doi.org/10.1785/0120190034 SN - 0037-1106 SN - 1943-3573 VL - 109 IS - 5 SP - 2036 EP - 2049 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Chen, Yen-Shin A1 - Weatherill, Graeme A1 - Pagani, Marco A1 - Cotton, Fabrice Pierre T1 - A transparent and data-driven global tectonic regionalization model for seismic hazard assessment JF - Geophysical journal international N2 - A key concept that is common to many assumptions inherent within seismic hazard assessment is that of tectonic similarity. This recognizes that certain regions of the globe may display similar geophysical characteristics, such as in the attenuation of seismic waves, the magnitude scaling properties of seismogenic sources or the seismic coupling of the lithosphere. Previous attempts at tectonic regionalization, particularly within a seismic hazard assessment context, have often been based on expert judgements; in most of these cases, the process for delineating tectonic regions is neither reproducible nor consistent from location to location. In this work, the regionalization process is implemented in a scheme that is reproducible, comprehensible from a geophysical rationale, and revisable when new relevant data are published. A spatial classification-scheme is developed based on fuzzy logic, enabling the quantification of concepts that are approximate rather than precise. Using the proposed methodology, we obtain a transparent and data-driven global tectonic regionalization model for seismic hazard applications as well as the subjective probabilities (e.g. degree of being active/degree of being cratonic) that indicate the degree to which a site belongs in a tectonic category. KW - Fuzzy logic KW - Earthquake hazards KW - Seismicity and tectonic Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy005 SN - 0956-540X SN - 1365-246X VL - 213 IS - 2 SP - 1263 EP - 1280 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Durand, Virginie A1 - Bentz, Stephan A1 - Kwiatek, Grzegorz A1 - Dresen, Georg A1 - Wollin, Christopher A1 - Heidbach, Oliver A1 - Martinez-Garzon, Patricia A1 - Cotton, Fabrice Pierre A1 - Nurlu, Murat A1 - Bohnhoff, Marco T1 - A two-scale preparation phase preceded an M-w 5.8 earthquake in the sea of marmara offshore Istanbul, Turkey JF - Seismological research letters N2 - We analyze the spatiotemporal evolution of seismicity during a sequence of moderate (an M-w 4.7 foreshock and M-w 5.8 mainshock) earthquakes occurring in September 2019 at the transition between a creeping and a locked segment of the North Anatolian fault in the central Sea of Marmara, northwest Turkey. To investigate in detail the seismicity evolution, we apply a matched-filter technique to continuous waveforms, thus reducing the magnitude threshold for detection. Sequences of foreshocks preceding the two largest events are clearly seen, exhibiting two different behaviors: a long-term activation of the seismicity along the entire fault segment and a short-term concentration around the epicenters of the large events. We suggest a two-scale preparation phase, with aseismic slip preparing the mainshock final rupture a few days before, and a cascade mechanism leading to the nucleation of the mainshock. Thus, our study shows a combination of seismic and aseismic slip during the foreshock sequence changing the strength of the fault, bringing it closer to failure. Y1 - 2020 U6 - https://doi.org/10.1785/0220200110 SN - 0895-0695 SN - 1938-2057 VL - 91 IS - 6 SP - 3139 EP - 3147 CY - Boulder ER - TY - JOUR A1 - Socquet, Anne A1 - Valdes, Jesus Pina A1 - Jara, Jorge A1 - Cotton, Fabrice Pierre 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 - Ziebarth, Malte J. A1 - von Specht, Sebastian A1 - Heidbach, Oliver A1 - Cotton, Fabrice Pierre A1 - Anderson, John G. T1 - Applying conservation of energy to estimate earthquake frequencies from strain rates and stresses JF - Journal of geophysical research : Solid earth N2 - Estimating earthquake occurrence rates from the accumulation rate of seismic moment is an established tool of seismic hazard analysis. We propose an alternative, fault-agnostic approach based on the conservation of energy: the Energy-Conserving Seismicity Framework (ENCOS). Working in energy space has the advantage that the radiated energy is a better predictor of the damage potential of earthquake waves than the seismic moment release. In a region, ENCOS balances the stationary power available to cause earthquakes with the long-term seismic energy release represented by the energy-frequency distribution's first moment. Accumulation and release are connected through the average seismic efficiency, by which we mean the fraction of released energy that is converted into seismic waves. Besides measuring earthquakes in energy, ENCOS differs from moment balance essentially in that the energy accumulation rate depends on the total stress in addition to the strain rate tensor. To validate ENCOS, we exemplarily model the energy-frequency distribution around Southern California. We estimate the energy accumulation rate due to tectonic loading assuming poroelasticity and hydrostasis. Using data from the World Stress Map and assuming the frictional limit to estimate the stress tensor, we obtain a power of 0.8 GW. The uncertainty range, 0.3-2.0GW, originates mainly from the thickness of the seismogenic crust, the friction coefficient on preexisting faults, and models of Global Positioning System (GPS) derived strain rates. Based on a Gutenberg-Richter magnitude-frequency distribution, this power can be distributed over a range of energies consistent with historical earthquake rates and reasonable bounds on the seismic efficiency. Y1 - 2020 U6 - https://doi.org/10.1029/2020JB020186 SN - 2169-9313 SN - 2169-9356 VL - 125 IS - 8 PB - American Geophysical Union CY - Washington ER -