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[SCG52-P04] What controls earthquake rupture complexity?: implications from the comparison of repeating earthquakes and other earthquakes.
Keywords:Source complexity, Fault maturity, Repeating earthquakes, Patch distribution
Earthquakes are natural phenomena that release the accumulated strain in the earth through fault slip. It is known that earthquakes can repeatedly occur at the same location. The asperity model (Lay & Kanamori, 1980), which accounts for various observations of plate boundaries, assumes that earthquakes occur only in limited areas (seismic patches) on the fault of which other parts slip aseismically. In the case of ordinary earthquakes, multiple patches may rupture together during a single earthquake, and the rupture area may not be the same for each repetition. On the other hand, special earthquakes called repeating earthquakes are considered to rupture the same single patch at each repetition. They are considered to occur at isolated patches, making it difficult to interact with other patches. Because of their characteristics, repeating earthquakes have been widely used to monitor the amount of aseismic slip on faults (e.g., Schaff et al., 1998; Uchida et al., 2004). However, it has been shown that even repeating earthquakes can change their rupture characteristics significantly after a large earthquake (Uchida et al., 2015).
This study systematically investigates the source complexity of repeating earthquakes in Japan. For this purpose, we estimated the source time functions of individual repeating earthquakes and used them to investigate the complexity of the rupture process. For comparison, we also examined the source complexity of crustal and intraslab earthquakes and interplate earthquakes other than repeating earthquakes.
We analyzed Mw3.5-5.5 earthquakes, which are listed in the F-net moment tensor catalog, for the period from 2003 to 2021 in eastern Japan. First, using the same method as Asano et al. (2011), we classified the earthquakes into three types based on the focal mechanisms and centroids: (1) interplate earthquakes, (2) crustal earthquakes, and (3) intraslab earthquakes. We deconvolved the seismic waveforms of each earthquake and estimated the source time function (Yoshida, 2019). We then evaluated the complexity of the source time functions by REEF (Ye et al., 2018) following Yoshida and Kanamori (2021).
The percentage of repeating earthquakes in the analyzed interplate earthquakes was about 60%. The REEF of repeating earthquakes tended to be even smaller than that of other interplate earthquakes; the 95% confidence range of median REEF of the repeating earthquakes is 2.7-2.9 (n=914), while that of the other interplate earthquakes is 3.2-3.7 (n=628). This result is consistent with the idea that repeating earthquakes have simpler rupture processes than regular earthquakes. On the other hand, some of the repeating earthquakes were found to have multiple peaks in their source time function. Some of them appeared to rupture the same combination of patches at each repetition, while others seemed to rupture a different number of patches. More detailed studies of the rupture process of repeating earthquakes are important.
We found that the REEFs of crustal and intraslab earthquakes tend to be smaller than that of interplate earthquakes. The 95% confidence range of median REEF of the crustal earthquakes is 4.0-4.3 (n=2662), while that of the intraslab earthquakes is 3.6-4.1 (n=1461). This result indicates that the slip distributions of interplate earthquakes tends to be simpler than those of earthquakes under other tectonics. This result is consistent with the inference based on the hypocenter distribution, suggesting that seismic patches on crustal faults are less isolated than those on interplate faults (Yoshida & Hasegawa, 2018, Tectonophysics). The difference of typical source complexity and the patch distribution may be related to the maturity of the fault. Our result may suggest that information on fault maturity can be extracted based on the rupture process and earthquake distribution on the fault.
This study systematically investigates the source complexity of repeating earthquakes in Japan. For this purpose, we estimated the source time functions of individual repeating earthquakes and used them to investigate the complexity of the rupture process. For comparison, we also examined the source complexity of crustal and intraslab earthquakes and interplate earthquakes other than repeating earthquakes.
We analyzed Mw3.5-5.5 earthquakes, which are listed in the F-net moment tensor catalog, for the period from 2003 to 2021 in eastern Japan. First, using the same method as Asano et al. (2011), we classified the earthquakes into three types based on the focal mechanisms and centroids: (1) interplate earthquakes, (2) crustal earthquakes, and (3) intraslab earthquakes. We deconvolved the seismic waveforms of each earthquake and estimated the source time function (Yoshida, 2019). We then evaluated the complexity of the source time functions by REEF (Ye et al., 2018) following Yoshida and Kanamori (2021).
The percentage of repeating earthquakes in the analyzed interplate earthquakes was about 60%. The REEF of repeating earthquakes tended to be even smaller than that of other interplate earthquakes; the 95% confidence range of median REEF of the repeating earthquakes is 2.7-2.9 (n=914), while that of the other interplate earthquakes is 3.2-3.7 (n=628). This result is consistent with the idea that repeating earthquakes have simpler rupture processes than regular earthquakes. On the other hand, some of the repeating earthquakes were found to have multiple peaks in their source time function. Some of them appeared to rupture the same combination of patches at each repetition, while others seemed to rupture a different number of patches. More detailed studies of the rupture process of repeating earthquakes are important.
We found that the REEFs of crustal and intraslab earthquakes tend to be smaller than that of interplate earthquakes. The 95% confidence range of median REEF of the crustal earthquakes is 4.0-4.3 (n=2662), while that of the intraslab earthquakes is 3.6-4.1 (n=1461). This result indicates that the slip distributions of interplate earthquakes tends to be simpler than those of earthquakes under other tectonics. This result is consistent with the inference based on the hypocenter distribution, suggesting that seismic patches on crustal faults are less isolated than those on interplate faults (Yoshida & Hasegawa, 2018, Tectonophysics). The difference of typical source complexity and the patch distribution may be related to the maturity of the fault. Our result may suggest that information on fault maturity can be extracted based on the rupture process and earthquake distribution on the fault.