Options
Segou, Margaret
Loading...
3 results
Now showing 1 - 3 of 3
- PublicationOpen AccessThe global aftershock zone(2014)
; ; ; ;Parsons, T.; USGS ;Marzocchi, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Segou, M.; Geosciences Azur; ; The aftershock zone of each large (M ≥ 7) earthquake extends throughout the shallows of planet Earth. Most aftershocks cluster near the mainshock rupture, but earthquakes send out shivers in the form of seismic waves, and these temporary distortions are large enough to trigger other earthquakes at global range. The aftershocks that happen at great distance from their mainshock are often superposed onto already seismically active regions, making them difficult to detect and understand. From a hazard perspective we are concerned that this dynamic process might encourage other high magnitude earthquakes, and wonder if a global alarm state is warranted after every large mainshock. From an earthquake process perspective we are curious about the physics of earthquake triggering across the magnitude spectrum. In this review we build upon past studies that examined the combined global response to mainshocks. Such compilations demonstrate significant rate increases during, and immediately after (~45 min) M N 7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M N 5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, recently published studies of individual large mainshocks associate M N 5 triggering at global range that is delayed by hours to days after surface wave arrivals. The longer the delay between mainshock and global aftershock, the more difficult it is to establish causation. To address these questions, we review the response to 260 M ≥ 7.0 shallow (Z ≤ 50 km) mainshocks in 21 global regions with local seismograph networks. In this way we can examine the detailed temporal and spatial response, or lack thereof, during passing seismic waves, and over the 24 h period after their passing. We see an array of responses that can involve immediate and widespread seismicity outbreaks, delayed and localized earthquake clusters, to no response at all. About 50% of the catalogs that we studied showed possible (localized delayed) remote triggering, and ~20% showed probable (instantaneous broadly distributed) remote triggering. However, in any given region, at most only about 2–3% of global mainshocks caused significant local earthquake rate increases. These rate increases are mostly composed of small magnitude events, and we do not find significant evidence of dynamically triggered M N 5 earthquakes. If we assume that the few observed M N 5 events are triggered, we find that they are not directly associated with surface wave passage, with first incidences being 9–10 h later. We note that mainshock magnitude, relative proximity, amplitude spectra, peak ground motion, and mainshock focal mechanisms are not reliable determining factors as to whether a mainshock will cause remote triggering. By elimination, azimuth, and polarization of surface waves with respect to receiver faults may be more important factors.157 112 - PublicationRestrictedToward a ground-motion logic tree for probabilistic seismic hazard assessment in Europe(2012-02-22)
; ; ; ; ; ; ; ; ; ; ; ; ; ;Delavaud, E.; ISTerre, Université Joseph Fourier, CNRS, BP 53, 38041 Grenoble, France ;Cotton, F.; ISTerre, Université Joseph Fourier, CNRS, BP 53, 38041 Grenoble, France ;Akkar, S.; Earthquake Engineering Research Center, Department of Civil Engineering, METU, 06531 Ankara, Turkey ;Scherbaum, F.; Institute of Earth and Environmental Sciences, University of Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Golm, Germany ;Danciu, L.; Swiss Seismological Service, Institute of Geophysics, ETH Zurich, Sonneggstrasse 5, NO, 8092 Zurich, Switzerland ;Beauval, C.; ISTerre, Université Joseph Fourier, CNRS, BP 53, 38041 Grenoble, France ;Drouet, S.; ISTerre, Université Joseph Fourier, CNRS, BP 53, 38041 Grenoble, France ;Douglas, J.; RIS/RSI, BRGM, 3 avenue C. Guillemin, BP 36009, 45060 Orléans Cedex 2, France ;Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Sandikkaya, M. A.; Earthquake Engineering Research Center, Department of Civil Engineering, METU, 06531 Ankara, Turkey ;Segou, M.; Earthquake Engineering Research Center, Department of Civil Engineering, METU, 06531 Ankara, Turkey ;Faccioli, E.; Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milan, Italy ;Theodoulidis, N.; ITSAK, P.O. Box 53, Finikas 55102 Thessaloniki, Greece; ; ; ; ; ; ; ; ; ; ; ; 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.258 20 - PublicationOpen AccessFaults Geometry and the Role of Fluids in the 2016-2017 Central Italy Seismic Sequence(2018)
; ; ; ; ; ; ; ; ;The 2016–2017 Central Italy seismic sequence ruptured overlapping normal faults of the Apennines mountain chain, in nine earthquakes with magnitude Mw > 5 within a few months. Here we investigate the structure of the fault system using an extensive aftershock data set, from joint permanent and temporary seismic networks, and 3-D Vp and Vp/Vs velocity models. We show that mainshocks nucleated on gently west dipping planes that we interpret as inverted steep ramps inherited from the late Pliocene compression. The two large shocks, the 24 August, Mw = 6.0 Amatrice and the 30 October, Mw = 6.5 Norcia occurred on distinct faults reactivated by high pore pressure at the footwall, as indicated by positive Vp/Vs anomalies. The lateral extent of the overpressurized volume includes the fault patch of the Norcia earthquake. The irregular geometry of normal faults together with the reactivated ramps leads to the kinematic complexity observed during the coseismic ruptures and the spatial distribution of aftershocks.166 27