Stress Release Process Along an Intraplate Fault Analogous to the Plate Boundary: A Case Study of the 2017 M5.2 Akita‐Daisen Earthquake, NE Japan

Abstract

Stress accumulation and release inside the plate remains poorly understood compared to that at the plate boundaries. Spatiotemporal variations in foreshock and aftershock activities can provide key constraints on time‐dependent stress and deformation processes inside the plate. The 2017 M5.2 Akita‐Daisen intraplate earthquake in NE Japan was preceded by intense foreshock activity and triggered a strong sequence of aftershocks. We examine the spatiotemporal distributions of foreshocks and aftershocks and determine the coseismic slip distribution of the mainshock. Our results indicate that seismicity both before and after the mainshock was concentrated on a planar structure with N‐S strike that dips steeply eastward. We observe a migration of foreshocks toward the mainshock rupture area, suggesting the possibility that foreshocks were triggered by aseismic phenomena preceding the mainshock rupture. The mainshock rupture propagated toward the north, showing less slip beneath foreshock regions. The stress drop of the mainshock was 1.4 MPa, and the radiation efficiency was 0.72. Aftershocks were intensely triggered near the edge of large coseismic slip regions where shear stress increased. The aftershock region expanded along the fault strike, which can be attributed to the postseismic aseismic slip of the mainshock. We find that the foreshocks, mainshock, aftershocks, and postseismic slip released stress at different segments along the fault, which may reflect differences in frictional properties. Obtained results were similar to those observed for interplate earthquakes, which supports the hypothesis that the deformation processes along plate boundaries and intraplate faults are fundamentally the same.

Fault‐Valve Behavior Estimated From Intensive Foreshocks and Aftershocks of the 2017 M 5.3 Kagoshima Bay Earthquake Sequence, Kyushu, Southern Japan

“…This relationship is consistent with the hypothesis that the mainshock rupture occurred in the seismic gap of the foreshock and aftershock activities. A similar spatial separation of the mainshock and foreshocks and aftershocks in the rupture area was also reported for a recent M5.2 intraplate earthquake in Akita, northeastern Japan (Yoshida, Taira, et al, 2020).…”

Resolution and uncertainties in estimates of earthquake stress drop and energy release

“…Detailed analyses are enabling precise characterization of exceptionally well recorded earthquakes (e.g. [73,168,190]), but for statistical analysis and ground motion prediction larger scale inversion of greater numbers of events is essential. Combining and developing the large scale inversion methods of Shearer et al [119] and Ross et al [191] with improved statistical analysis of the uncertainties and biases caused by simplifying assumptions and methods (e.g.…”

The 2021 Mw7.0 and Mw6.7 Miyagi‐Oki Earthquakes Nucleated in a Deep Seismic/Aseismic Transition Zone: Possible Effects of Transient Instability Due To the 2011 Tohoku Earthquake

“…We use 297,655 P-wave and 293,579 S-wave differential arrival time data calculated from the arrival time data in the JMA unified catalog, which we call catalog-derived data. We also use 10,151,148 P-waves and 5,861,433 S-wave differential arrival time data derived from waveform correlation analysis using the same method as Yoshida et al (2020), which we call correlation-derived data. Details of the waveform correlation analysis are described in Text S1 in Supporting Information S1.…”