
Stress drops for intermediate‐depth intraslab earthquakes beneath H okkaido, northern J apan: Differences between the subducting oceanic crust and mantle events
Author(s) -
Kita Saeko,
Katsumata Kei
Publication year - 2015
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2014gc005603
Subject(s) - geology , crust , oceanic crust , seismology , mantle (geology) , subduction , pacific plate , drop (telecommunication) , convergent boundary , tectonics , geophysics , telecommunications , computer science
Spatial variations in the stress drop for 1726 intermediate‐depth intraslab earthquakes were examined in the subducting Pacific plate beneath Hokkaido, using precisely relocated hypocenters, the corner frequencies of events, and detailed determined geometry of the upper interface of the Pacific plate. The results show that median stress drop for intraslab earthquakes generally increases with an increase in depth from ∼10 to 157 Mpa at depths of 70–300 km. More specifically, median stress drops for events in the oceanic crust decrease (9.9–6.8 MPa) at depths of 70–120 km and increase (6.8–17 MPa) at depths of 120–170 km, whereas median stress drop for events in the oceanic mantle decrease (21.6–14.0 MPa) at depths of 70–170 km, where the geometry of the Pacific plate is well determined. The increase in stress drop with depth in the oceanic crust at depths of 120–170 km, for which several studies have shown an increase in velocity, can be explained by an increase in the velocity and a decrease in the water content due to the phase boundary with dehydration in the oceanic crust. Stress drops for events in the oceanic mantle were larger than those for events in the oceanic crust at depths of 70–120 km. Differences in both the rigidity of the rock types and in the rupture mechanisms for events between the oceanic crust and mantle could be causes for the stress drop differences within a slab.