Coseismic deformation field derived from Sentinel-1A data and slip inversion of the 2015 Chile Mw8.3 earthquake
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Abstract. We obtain the coseismic surface deformation fields caused by the Chile Mw8.3 earthquake on 16 September 2015 through analyzing Sentinel-1A/IW InSAR data from ascending and descending tracks. The results show that the main deformation field looks like a half circle convex to east with maximum coseismic displacement of about 1.33 m in descending LOS direction, 1.32 m in ascending LOS direction. Based on an elastic dislocation model in a homogeneous elastic half space, we construct a small-dip single plane fault model and invert the coseismic fault slip using ascending and descending Sentinel-1A/IW data separately and jointly. The results show that the patterns of the main slip region are similar in all datasets, but the scale of slip from ascending inversion is relatively smaller. Joint inversion can display comprehensive fault slip. The seismic moment magnitude from the joint inversion is Mw8.25, the rupture length along strike is about 340 km with a maximum slip of 8.16 m near the trench located at –31.04 N, –72.49 E, and the coseismic slip mainly concentrates at shallow depth above the hypocenter with a symmetry shape. The depth where coseismic slip is near zero appears to a depth of 50 km, quantitatively indicating the down-dip limit of the seismogenic zone. From the calculated coseismic Coulomb stress change, we find aftershocks locations correlate well with the areas having increased Coulomb stress and most areas with increased Coulomb stress appeared beneath the main shock fault plane.Keywords:
Hypocenter
Magnetic dip
Moment magnitude scale
Epicenter
Seismic moment
The parameters of the hypocenter of the Bilimbaev earthquake that occurred on August 17, 1914, are located. We performed earthquake location based on our compilation of all available seismological bulletins of the time that included data from the ISC-GEM (International Seismological Centre–Global Earthquake Model) project, the EuroSeismos project, and the Geophysical Survey of the Russian Academy of Sciences. The location was performed using a modified generalized beamforming method based on the ak135 travel time model and regional model by the Ural region. The new epicenter is removed from the epicenters, previous-ly determined from macroseismic and partly instrumental data, at a distance not exceeding 28 km. The previously calculated earthquake epicenters are in the region of the error ellipse of the new epicenter. The depth values indicated earlier also lie in the range of possible depths of the focus of the specified hypocenter. Thus, all the epicenters, including the new one, are relevant and with equal probability can be considered as the true epicenter of the earthquake
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Abstract After the 2011 M9 Tohoku earthquake, several interplate earthquakes of Mw 6 occurred in close proximity in the area off the northern Miyagi prefecture in Japan, including the 2015 Mw 6.8 earthquake. To advance our understanding of the similarity and diversity in earthquake ruptures at the same asperity, this study compares the source processes of six Mw 6.0–6.8 earthquakes in this region. The results of hypocenter relocation and source process inversion show that these Mw 6.0–6.8 events repeatedly ruptured the same patch west of their hypocenters; the rupture always began in this patch and tended to propagate westward. Moment releases for this patch are similar, approximately Nm (Mw 6.3) before and after the Tohoku earthquake. However, the Mw 6.0 event that occurred 20 days after the Tohoku earthquake had only half this moment release, likely reflecting less than usual healing of frictional strength. Moreover, the fourth earthquake after the Tohoku earthquake, which is the 2015 Mw 6.8 earthquake, released a much larger moment of Nm (Mw 6.5) in the same patch and caused a subsequent large slip in a second patch to the east. The presence of the eastern hidden patch likely affected the slip amount of the western patch that typically causes Mw 6.3 events. An examination of M JMA 2.0–5.3 repeating earthquake activity suggests that this eastern patch also affected the preparation period for the 2015 event. The present observation suggests that even locations with well‐predetermined rupture areas and slips can produce much larger slips than usual under the presence of adjacent hidden slip patches.
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Seismic moment
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Asperity (geotechnical engineering)
Slow earthquake
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Abstract. In this paper we present the procedure for earthquake location and characterization implemented in the Italian candidate Tsunami Service Provider at INGV in Roma. Following the ICG/NEAMTWS guidelines, the first tsunami warning messages are based only on seismic information, i.e. epicenter location, hypocenter depth and magnitude, which are automatically computed by the software Early-est. Early-est is a package for rapid location and seismic/tsunamigenic characterization of earthquakes. The Early-est software package operates on offline-event or continuous-realtime seismic waveform data to perform trace processing and picking, and, at a regular report interval, phase association, event detection, hypocenter location, and event characterization. In this paper we present the earthquake parameters computed by Early-est from the beginning of 2012 till the end of December 2014 at global scale for events with magnitude M ≥ 5.5, and the detection timeline. The earthquake parameters computed automatically by Early-est are compared with reference manually revised/verified catalogs. From our analysis the epicenter location and hypocenter depth parameters do not differ significantly from the values in the reference catalogs. The epicenter coordinates generally differ less than 20 ∓ 20 km from the reference epicenter coordinates; focal depths are less well constrained and differ generally less than 0 ∓ 30 km. Early-est also provides mb, Mwp and Mwpd magnitude estimations. mb magnitudes are preferred for events with Mwp ≲ 5.8, while Mwpd are valid for events with Mwp ≳ 7.2. The magnitude mb show wide differences with respect to the reference catalogs, we thus apply a linear correction mbcorr = mb · 0.52 + 2.46, such correction results into δmb ≈ 0.0 ∓ 0.2 uncertainty with respect the reference catalogs. As expected the Mwp show distance dependency. Mwp values at stations with epicentral distance Δ ≲ 30° are significantly overestimated with respect the CMT-global solutions, whereas Mwp values at stations with epicentral distance Δ ≳ 90° are slightly underestimated. We thus apply a 3rd degree polynomial distance correction. After applying the distance correction, the Mwp provided by Early-est differs from CMT-global catalog values of about δ Mwp ≈ 0.0 ∓ 0.2. Early-est continuously acquires time series data and updates the earthquake source parameters. Our analysis shows that the epicenter coordinates and the magnitude values converge rather quickly toward the final values. Generally we can provide robust and reliable earthquake source parameters to compile tsunami warning message within less than about 15 min after event origin time.
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