Source parameters and radiation efficiency for intermediate-depth earthquakes in Northeast Japan

Abstract

We estimated source parameters of 216 intermediate-depth (65-150 km) earthquakes (M w 4.0-7.0) in the Pacific slab beneath Japan along using Hi-net data. We made determinations of static stress drop, radiated energy and radiation efficiency, along with estimates of the whole path attenuation, to study the source scaling as a function of earthquake size and depth. Our results show that there is a small increase in the values of the ratio of radiated energy to seismic moment, as a function of seismic moment, which is due to an associated slight increase of static stress drop with earthquake size. We also estimated the radiation efficiency for these events using the static stress drops and radiated energies. The values of radiation efficiency are slightly lower compared to shallow crustal earthquakes. These results indicate that dissipative energy processes may be relatively more important for intermediate-depth earthquakes.

Source Parameter Variability of Intermediate‐Depth Earthquakes in Japanese Subduction Zones

“…The mean stress drops for both regions range from around 16–60 MPa (somewhere between 20 and 30 MPa for most data selection tests). These values for the Hokkaido region are in agreement with previous results from Kita and Katsumata () and from Nishitsuji and Mori (). We find no significant variation of stress drop with depth for either single region, though it must be noted that we have confined our study to earthquakes in a narrow depth range (see, e.g., Figures S9 and S10).…”

“…Plotting the radiated efficiency (Figures and ), however, shows a large scatter with no clear trend, perhaps a minor decrease in stress drop with moment for the Hokkaido data set that is not statistically significant (it is difficult to regress a line). The majority of radiated efficiencies (Figures and ) range from 0.04 to about 0.11 for the Brune model tests, which is lower than for shallow events, and consistent with the general observations of intraslab earthquakes (Ko & Kuo, ; Nishitsuji & Mori, ). There is not a significant difference in the radiated efficiency between the two regions, nor, as mentioned, is there any significant trend with moment.…”

“…We are interested in constraining the mechanisms of intermediate‐depth earthquakes, and we have determined that there is a robust scaling of stress drop with moment at intermediate depth in both the Pacific Trench in Hokkaido and the Philippine Sea Plate in Kyushu, the former of which where we see a relatively cold subducting slab displaying a double seismic zone. The scaling in the Pacific Plate is in agreement with what has been found in other studies of intermediate‐depth earthquakes (Prieto et al, ; Nishitsuji & Mori, ). In Kyushu, there is a slightly warmer slab without a double seismic zone and much denser concentration of earthquakes, but the source parameters resemble those of Hokkaido—scaling stress drops accommodated by scaling apparent stress.…”

Global rupture parameters for deep and intermediate‐depth earthquakes

“…The stress drop shows a slight increase as a function of moment, given by the equation . The scaling of stress drop is in agreement with previous work on intermediate‐depth earthquakes [ Prieto et al ., ; Nishitsuji and Mori , ] and comes naturally from the moment scaling of rupture duration observed for deep earthquakes. The apparent stress also increases as .…”

The 19 September 2017 (Mw7.1) Intermediate‐Depth Mexican Earthquake: A Slow and Energetically Inefficient Deadly Shock

“…Thermal shear runaway in the focal region can generate highly localized ductile deformation and slip instabilities (Kanamori et al, 1998;Prieto et al, 2012). Recently, local and global seismological studies have shown that most of IDEs have a low radiation efficiency, suggesting that thermal shear runaway is the leading source mechanism of IDEs (Díaz-Mojica et al, 2014;Nishitsuji & Mori, 2013;Prieto et al, 2013Prieto et al, , 2017. Recently, local and global seismological studies have shown that most of IDEs have a low radiation efficiency, suggesting that thermal shear runaway is the leading source mechanism of IDEs (Díaz-Mojica et al, 2014;Nishitsuji & Mori, 2013;Prieto et al, 2013Prieto et al, , 2017.…”