5:15 PM - 6:30 PM
[SCG50-P09] Non-double-couple earthquake in the focal area of the 2000 Western Tottori earthquake by “0.1 manten” hyperdense seismic observation
Keywords:inland earthquake, Non-double-couple earthquakes
Non-double-couple (NDC) earthquakes are defined as a faulting of ordinary double-couple (DC) earthquake on a fault associated with additional rupture at the hypocenter. They have been mainly observed in volcanic zones and interpreted as faulting related to fluid effects in the hypocentral region. Study on NDC earthquakes is important for understanding the faulting process and provides an opportunity to obtain new information on stress and strength of the Earth’s crust.
In the focal area of the 2000 Western Tottori earthquake (M7.3), Yukutake et al. (2017) showed 8 best fit fault planes, suggesting the aftershock sequence was attributed to complex fault system. In order to investigate states of stress and strength in the large earthquake in detail, we have deployed 1,000 temporary seismic stations in and around the source region of the earthquake during the period from April 2017 to April 2018. This observation is called “0.1 manten” hyperdense seismic observation. We determined hypocenters and focal mechanisms using the data of the seismic network of both the “0.1 manten” and Hi-net by NIED. The data we analyze is both manually and automatically picked the arrival times and polarities of first P wave onset. Hayashida et al. (2020) found that the observational polarity distribution was slightly different from that expected by a DC source model at certain areas. In this study, we attempted to obtain spatial characteristic of the NDC events from the precise moment tensor solution. By following the processing in the previous study, we adopted the tensile-shear model and searched optimal model by performing a grid search and correlation analysis of S/P wave amplitude ratio. In addition, we introduced a weighting factor to homogenize the distribution of polarities on a focal sphere of an event in the NDC detection.
We found a trend that magnitude of NDC component become small as hypocenter was distant from the fault plan and located at edges of the faults plane. In addition, few earthquakes with large NDC components have large magnitude.
In the focal area of the 2000 Western Tottori earthquake (M7.3), Yukutake et al. (2017) showed 8 best fit fault planes, suggesting the aftershock sequence was attributed to complex fault system. In order to investigate states of stress and strength in the large earthquake in detail, we have deployed 1,000 temporary seismic stations in and around the source region of the earthquake during the period from April 2017 to April 2018. This observation is called “0.1 manten” hyperdense seismic observation. We determined hypocenters and focal mechanisms using the data of the seismic network of both the “0.1 manten” and Hi-net by NIED. The data we analyze is both manually and automatically picked the arrival times and polarities of first P wave onset. Hayashida et al. (2020) found that the observational polarity distribution was slightly different from that expected by a DC source model at certain areas. In this study, we attempted to obtain spatial characteristic of the NDC events from the precise moment tensor solution. By following the processing in the previous study, we adopted the tensile-shear model and searched optimal model by performing a grid search and correlation analysis of S/P wave amplitude ratio. In addition, we introduced a weighting factor to homogenize the distribution of polarities on a focal sphere of an event in the NDC detection.
We found a trend that magnitude of NDC component become small as hypocenter was distant from the fault plan and located at edges of the faults plane. In addition, few earthquakes with large NDC components have large magnitude.