Abstract We perform kinematic and dynamic source inversions of four interplate thrust earthquakes... more Abstract We perform kinematic and dynamic source inversions of four interplate thrust earthquakes that occurred near the trench at the base of the continental wedge in Northern Chile and we compare them to deeper intraplate events. The magnitudes of these interplate events were between Mw 6.3 and Mw 6.5, with hypocentral depths varying between 17.8 km and 28 km. These earthquakes correspond to one foreshock and three aftershocks of the large 2014 Mw 8.2 Iquique earthquake. The geometry of the seismic rupture obtained from the kinematic and dynamic inversions were similar for the four earthquakes studied and their dynamic source parameters are in accordance with typical interplate earthquakes around Mw 6.5. We compare the dynamic rupture of these events with those of five intraplate, intermediate-depth earthquakes that occurred in Northern Chile, Japan, Argentina and Mexico with depths between 57 km and 250 km. We also compare these events with the Mw 6.9 Valparaiso earthquake that was also a shallow interplate thrust event. Results show that the main dynamic parameters of the interplate events (stress in the nucleation zone, overall stress drop and fracture energy rate) were smaller than those of the intraplate intermediate-depth earthquakes. Furthermore, we compare our results with those obtained with several methodologies commonly used to estimate values of stress drop, fault radius and corner frequency. We find some minor differences between them for most of the earthquakes analyzed. Finally, we infer from our results that the studied area, located in the subduction interface zone near the trench, is suitable for earthquake nucleation of small to moderate earthquakes and does not represent a barrier for a future large tsunamigenic rupture.
This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis an... more This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis and on the Tohoku earthquake. It proposes a detailed description of the French situation (in the West Indies, in metropolitan France, and in terms of soil response), and a discussion of social and economic issues (governance, seismic regulation and nuclear safety, para-seismic protection of constructions). The report is completed by other large documents: presentation of data on the Japanese earthquake, discussion on prediction and governance errors in the management of earthquake mitigation in Japan, discussions on tsunami prevention, on needs of research on accelerometers, and on the seismic risk in France
On 20 January 2019, the Chilean cities of Coquimbo and La Serena were shaken by an intraplate ear... more On 20 January 2019, the Chilean cities of Coquimbo and La Serena were shaken by an intraplate earthquake of Mw 6.7 located at 70 km depth. High peak ground acceleration values and macroseismic intensities were reported. The mainshock was followed by more than 150 aftershocks higher than ML 2.5, a seismic sequence completely recorded by local stations. Using a 3D velocity model, we precisely located the seismicity. The aftershocks were located some 20 km above and shifted from the mainshock but still inside the Nazca plate. We also performed moment tensor inversion of nine events obtaining mostly normal‐fault focal mechanisms and kinematic inversions using the elliptical‐patch approach. We found that the mainshock broke an approximated zone of 6 km by 8 km, propagated upward in the northwest direction and away from the aftershock area. The rupture inverted from accelerograms containing up to 1 Hz was characterized with a high stress drop of 7.51 MPa and a short seismic source time fu...
The Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the l... more The Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the last mega‐earthquake occurred in 1730. Intense seismicity started 2 days before the Mw 6.9 mainshock, a slow trenchward movement was observed in the coastal GPS antennas and was accompanied by foreshocks and repeater‐type seismicity. To characterize the rupture process of the mainshock, we perform a dynamic inversion using the strong‐motion records and an elliptical patch approach. We suggest that a slow slip event preceded and triggered the Mw 6.9 earthquake, which ruptured an elliptical asperity (semiaxis of 10 km and 5 km, with a subshear rupture, stress drop of 11.71 MPa, yield stress of 17.21 MPa, slip weakening of 0.65 m, and kappa value of 1.98). This earthquake could be the beginning of a long‐term nucleation phase to a major rupture, within the highly coupled Central Chile zone where a megathrust earthquake like 1730 is expected.
Abstract We perform kinematic and dynamic source inversions of four interplate thrust earthquakes... more Abstract We perform kinematic and dynamic source inversions of four interplate thrust earthquakes that occurred near the trench at the base of the continental wedge in Northern Chile and we compare them to deeper intraplate events. The magnitudes of these interplate events were between Mw 6.3 and Mw 6.5, with hypocentral depths varying between 17.8 km and 28 km. These earthquakes correspond to one foreshock and three aftershocks of the large 2014 Mw 8.2 Iquique earthquake. The geometry of the seismic rupture obtained from the kinematic and dynamic inversions were similar for the four earthquakes studied and their dynamic source parameters are in accordance with typical interplate earthquakes around Mw 6.5. We compare the dynamic rupture of these events with those of five intraplate, intermediate-depth earthquakes that occurred in Northern Chile, Japan, Argentina and Mexico with depths between 57 km and 250 km. We also compare these events with the Mw 6.9 Valparaiso earthquake that was also a shallow interplate thrust event. Results show that the main dynamic parameters of the interplate events (stress in the nucleation zone, overall stress drop and fracture energy rate) were smaller than those of the intraplate intermediate-depth earthquakes. Furthermore, we compare our results with those obtained with several methodologies commonly used to estimate values of stress drop, fault radius and corner frequency. We find some minor differences between them for most of the earthquakes analyzed. Finally, we infer from our results that the studied area, located in the subduction interface zone near the trench, is suitable for earthquake nucleation of small to moderate earthquakes and does not represent a barrier for a future large tsunamigenic rupture.
This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis an... more This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis and on the Tohoku earthquake. It proposes a detailed description of the French situation (in the West Indies, in metropolitan France, and in terms of soil response), and a discussion of social and economic issues (governance, seismic regulation and nuclear safety, para-seismic protection of constructions). The report is completed by other large documents: presentation of data on the Japanese earthquake, discussion on prediction and governance errors in the management of earthquake mitigation in Japan, discussions on tsunami prevention, on needs of research on accelerometers, and on the seismic risk in France
On 20 January 2019, the Chilean cities of Coquimbo and La Serena were shaken by an intraplate ear... more On 20 January 2019, the Chilean cities of Coquimbo and La Serena were shaken by an intraplate earthquake of Mw 6.7 located at 70 km depth. High peak ground acceleration values and macroseismic intensities were reported. The mainshock was followed by more than 150 aftershocks higher than ML 2.5, a seismic sequence completely recorded by local stations. Using a 3D velocity model, we precisely located the seismicity. The aftershocks were located some 20 km above and shifted from the mainshock but still inside the Nazca plate. We also performed moment tensor inversion of nine events obtaining mostly normal‐fault focal mechanisms and kinematic inversions using the elliptical‐patch approach. We found that the mainshock broke an approximated zone of 6 km by 8 km, propagated upward in the northwest direction and away from the aftershock area. The rupture inverted from accelerograms containing up to 1 Hz was characterized with a high stress drop of 7.51 MPa and a short seismic source time fu...
The Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the l... more The Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the last mega‐earthquake occurred in 1730. Intense seismicity started 2 days before the Mw 6.9 mainshock, a slow trenchward movement was observed in the coastal GPS antennas and was accompanied by foreshocks and repeater‐type seismicity. To characterize the rupture process of the mainshock, we perform a dynamic inversion using the strong‐motion records and an elliptical patch approach. We suggest that a slow slip event preceded and triggered the Mw 6.9 earthquake, which ruptured an elliptical asperity (semiaxis of 10 km and 5 km, with a subshear rupture, stress drop of 11.71 MPa, yield stress of 17.21 MPa, slip weakening of 0.65 m, and kappa value of 1.98). This earthquake could be the beginning of a long‐term nucleation phase to a major rupture, within the highly coupled Central Chile zone where a megathrust earthquake like 1730 is expected.
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Papers by Raul Madariaga