Spatio-temporal Characteristics of Frictional Properties on the Subducting Pacific Plate Off the East of Tohoku District, Japan Estimated from Stress Drops of Small Earthquakes

Abstract

<jats:title>Abstract</jats:title> <jats:p>The east coast of the Tohoku district, Japan has a high seismicity, including aftershocks of the 2011 M9 Tohoku earthquake. We analyzed 1142 earthquakes with $4.4 \le M_{W} \le 5.0$ that occurred in 2003 through 2018 and obtained spatio-temporal pattern of stress drop on the Pacific Plate that subducts beneath the Okhotsk Plate. Here we show that small earthquakes at edges of a region with a large slip during the 2011 Tohoku earthquake had high values of stress drop, indicating that the areas had a high frictional strength and suppressed the coseismic slip of the 2011 Tohoku earthquake. In addition, stress drops of small earthquakes in some of the areas likely decreased after the 2011 Tohoku earthquake. This indicates that the frictional strength decreased at the areas due to the following aftershocks of the 2011 Tohoku earthquake, consistent with a high aftershock activity. This also supports that the frictional properties on a subducting plate interface can be monitored by stress drops of small earthquakes, as pointed out by some previous studies.</jats:p>

Spatio‐Temporal Evolution of Earthquake Static Stress Drop Values in the 2016–2017 Central Italy Seismic Sequence

“…Consistent interpretations by Yamada et al. (2021) associated high stress drop values with a gradual weakening of the shear strength due to stress concentration during the coseismic slip of the mainshocks. Following the temporal decrease, the median $$\hat{{\Delta}\sigma }$$ values then increase in the subsequent months, consistent with fault zone healing and an increase in fault strength (e.g., Goebel et al., 2015; Moyer et al., 2018; Vidale et al., 1994).…”

Spatio‐Temporal Evolution of Aftershock and Repeater Source Properties After the 2016 Pedernales Earthquake (Ecuador)

“…A ratio of 1.27 corresponds to a rupture velocity of about 0.75 $${v}_{s}$$, so we set k P as 0.33 and k S as 0.26 (Kaneko & Shearer, 2014) to compute the stress drops (4). Other studies have found similar $${{v}_{r}/v}_{s}$$ based on P / S corner frequency ratios in subduction zones (Yamada et al., 2021). Note however that this ratio is an average in space and time, and therefore the scattering can be explained by varying rupture velocities and geometries among events.…”

“…Some authors have found a degree of correlation between stress drops of microearthquakes and the coseismic slip areas of large earthquakes: stress drops were sometimes found to be high around past rupture zones and low within them (Yamada et al., 2021), although that correlation is ambiguous (Allmann & Shearer, 2007; Shearer et al., 2006). Similarly, Hardebeck and Aron (2009) found that stress drops of earthquakes in and around locked zones were higher on average than those on creeping portions of the Hayward fault (California) at similar depths, suggesting a link to coupling.…”