Abstract
ᅟWe show that the spatial heterogeneity in the coseismic displacement of large earthquakes likely reflects the spatial characteristics of the frictional properties and that it can be inferred from the stress drop of moderate-sized earthquakes. We analyzed stress drops of 686 earthquakes with magnitudes of 4.0 to 5.0 off the south-east of Hokkaido, Japan, and investigated the spatial heterogeneity between the difference of shear strength and dynamic stress level on the Pacific Plate. We deconvolved observed P and S waves with those of collocated small earthquakes and derived the source effect of the earthquakes. We then estimated the corner frequencies of the earthquakes and calculated stress drops using a circular fault model. The values of stress drops showed a spatial pattern consistent with slip distributions of historical large earthquakes. Earthquakes that occurred in the area with a large coseismic slip during the 1968 Tokachi-oki (MW 8.2) and the 2003 Tokachi-oki (MW 8.0) earthquakes had large values of stress drop, whereas earthquakes in the afterslip area of the 2003 Tokachi-oki earthquake showed smaller values. In addition, an area between coseismic ruptures of the 1973 Nemuro-oki (MW 7.8) and the 2003 Tokachi-oki earthquakes had a large value of stress drop. Ruptures occurred in this area during the 1952 Tokachi-oki earthquake (MW 8.1), and the area acted as a barrier during the 2003 Tokachi-oki earthquake. These facts suggest that the frictional properties of the plate interface show little temporal change, and their spatial pattern can be monitored by stress drops of moderate-sized earthquakes. The spatial heterogeneity provides important information for estimating the slip pattern of a future large earthquake and discussing a policy for disaster mitigation, especially for regions in which slip patterns of historical large earthquakes are unclear.Graphical abstract
Highlights
Numerous large earthquakes have been observed off the south-east of Hokkaido, Japan, due to the subduction of the Pacific Plate beneath the Okhotsk Plate at a rate of 80–100 mm/year (e.g., DeMets et al 1990)
These results suggest that stress drops of earthquakes represent in situ frictional properties, which is consistent with previous studies
Spatial patterns of stress drop for both results estimated from P and S waves suggest correlations with slip distributions of large historical earthquakes and an afterslip following the 2003 Tokachi-oki earthquake
Summary
Numerous large earthquakes have been observed off the south-east of Hokkaido, Japan, due to the subduction of the Pacific Plate beneath the Okhotsk Plate at a rate of 80–100 mm/year (e.g., DeMets et al 1990). Yagi (2004) analyzed the source rupture process of the 2003 Tokachi-oki earthquake (in Japanese, X-oki means “off the coast of X”) and found that an area with a large coseismic slip in the shallower part had a longer rise time than the area in the deeper part of the fault plane. They pointed out that the difference should be attributed to the spatial variety of the frictional properties. They found that areas with a significant afterslip were located around the coseismic rupture area, especially at the shallower plate
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
