Cascading elastic perturbation in Japan due to the 2012 Mw 8.6 Indian Ocean earthquak

Andrew A. Delorey,1 Kevin Chao,2 Kazushige Obara,3 Paul A. Johnson1

1 Los Alamos National Laboratory 2 Massachusetts Institute of Technology 3 Earthquake Research Institute, The University of Tokyo

 

Science Advances, 16 Oct 2015, Vol. 1, no. 9, e1500468, DOI: 10.1126/sciadv.1500468

 

Cascading elastic perturbation in Japan due to the 2012 Mw 8.6 Indian Ocean earthquake

 

  Since the discovery of extensive earthquake triggering occurring in response to the 1992 Mw (moment magnitude) 7.3 Landers earthquake, it is now well established that seismic waves from earthquakes can trigger other earthquakes, tremor, slow slip, and pore pressure changes. Our contention is that earthquake triggering is one manifestation of a more widespread elastic disturbance that reveals information about Earth’s stress state. Earth’s stress state is central to our understanding of both natural and anthropogenic-induced crustal processes. We show that seismic waves from distant earthquakes may perturb stresses and frictional properties on faults and elastic moduli of the crust in cascading fashion. Transient dynamic stresses place crustal material into a metastable state during which the material recovers through a process termed slow dynamics. This observation of widespread, dynamically induced elastic perturbation, including systematic migration of offshore seismicity, strain transients, and velocity transients, presents a new characterization of Earth’s elastic system that will advance our understanding of plate tectonics, seismicity, and seismic hazards.

 

Fig. 1 Maps. (A and B) These maps show (A) the IOE and (B) our study area in Japan. Symbols in (B) are as follows: blue and green triangles are Hi-net stations used to calculate seismic velocities; green stations are used to calculate seismic coherence. Red circles are the epicenters of the 2011 TOE and shallow earthquakes discussed in the text. Black triangles are F-net station HRO and extensometer KTA. Inset shows location of shallow earthquakes; hatch marks indicate region where seismic velocities are calculated.
Fig. 1 Maps. (A and B) These maps show (A) the IOE and (B) our study area in Japan. Symbols in (B) are as follows: blue and green triangles are Hi-net stations used to calculate seismic velocities; green stations are used to calculate seismic coherence. Red circles are the epicenters of the 2011 TOE and shallow earthquakes discussed in the text. Black triangles are F-net station HRO and extensometer KTA. Inset shows location of shallow earthquakes; hatch marks indicate region where seismic velocities are calculated.
Fig. 2 Observations. (A) Earthquakes (origin 31.32°N, 134.10°E). Red triangles represent P1 and P2 (top to bottom). Blue triangle represents P0. Black vertical line extending through all subfigures is IOE. (B) Stacked interstation seismic coherence. (C) Cumulative aftershocks for P0 and P2 (black stars) with map view inset. Blue and red curves are cumulative number of earthquakes in the P0 and P2 clusters, respectively. The P0 main shock and northern aftershocks (blue dots) generally precede the P2 main shock and aftershocks (red dots), and the P0 southern aftershocks (red dots). Vertical dashed lines mark P0 (blue, left) and P2 (red), and initiation time of earthquake cluster following P0 (blue, right). (D) Stacked fractional change in interstation travel times with 1 SD; red shaded area indicates time period where travel time decrease may have initiated. (E) Volumetric strain at extensometer KTA.
Fig. 2 Observations. (A) Earthquakes (origin 31.32°N, 134.10°E). Red triangles represent P1 and P2 (top to bottom). Blue triangle represents P0. Black vertical line extending through all subfigures is IOE. (B) Stacked interstation seismic coherence. (C) Cumulative aftershocks for P0 and P2 (black stars) with map view inset. Blue and red curves are cumulative number of earthquakes in the P0 and P2 clusters, respectively. The P0 main shock and northern aftershocks (blue dots) generally precede the P2 main shock and aftershocks (red dots), and the P0 southern aftershocks (red dots). Vertical dashed lines mark P0 (blue, left) and P2 (red), and initiation time of earthquake cluster following P0 (blue, right). (D) Stacked fractional change in interstation travel times with 1 SD; red shaded area indicates time period where travel time decrease may have initiated. (E) Volumetric strain at extensometer KTA.

 

Fig. 3 Interpretation. (A to C) Cycle of stress transfer from (A) plate interface to shallow fore arc (B) resulting in normal faulting earthquakes and (C) stress transfer to interior Honshu Island. Blue triangles represent Hi-net stations. Red stars are normal faulting earthquakes.
Fig. 3 Interpretation.
(A to C) Cycle of stress transfer from (A) plate interface to shallow fore arc (B) resulting in normal faulting earthquakes and (C) stress transfer to interior Honshu Island. Blue triangles represent Hi-net stations. Red stars are normal faulting earthquakes.