5:00 PM - 5:15 PM
[S13-4-03] Bayesian inference of centroid moment tensors of the April 2016, Kumamoto (Kyushu, Japan), earthquake sequence
On 2016 April 16, Kumamoto prefecture in Kyushu region, Japan, was devastated by a shallow M7.3 earthquake. The seismic activity in the region started by foreshocks 28 hours before the main shock. The series of foreshocks have origin in Hinagu fault zone intersecting the main event's Futagawa fault zone Hence, the tectonic background for this earthquake is rather complex.
We computed centroid moment tensors (CMTs) for 11 events with M between 4.8 and 6.5, using the strong motion records of K-NET, KiK-net and F-net networks. We used the innovative Bayesian full-waveform inversion, ISOLA-ObsPy, which takes into account uncertainty of the velocity model structure. Such approach allows us to assess uncertainty of the inverted moment tensors.
The moment tensors show significant spatial variations. Dip-slip events are connected to the N-S extensional tectonic regime and right-lateral strike-slip events are linked to the NE-SW shear zone (Median Tectonic Line). Strike-slip events located close to the intersection of Hinagu and Futagawa fault zone are dipping slightly to east, while those in the southern area (Hinagu fault zone) are dipping to west. Most of events contain only minor CLVD component, which is statistically insignificant and can be related to the velocity model uncertainty. Nevertheless, two of the CMTs involve significantly large CLVD component (~30%), which may reflect complex rupture process. Decomposition of those moment tensors into two pure-shear moment tensors is non-unique. Nevertheless, preserving T-axis of the decomposed moment tensors suggests combined right-lateral strike-slip and dip-slip mechanisms, which are consistent with the tectonic settings of the intersection of the Hinagu and Futagawa fault zones. Finally, the Bayesian full-waveform inversion of CMTs of the Kumamoto earthquake sequence demonstrates the abilities of such a methodology, and suggests complex tectonic background for this earthquake sequence.
We computed centroid moment tensors (CMTs) for 11 events with M between 4.8 and 6.5, using the strong motion records of K-NET, KiK-net and F-net networks. We used the innovative Bayesian full-waveform inversion, ISOLA-ObsPy, which takes into account uncertainty of the velocity model structure. Such approach allows us to assess uncertainty of the inverted moment tensors.
The moment tensors show significant spatial variations. Dip-slip events are connected to the N-S extensional tectonic regime and right-lateral strike-slip events are linked to the NE-SW shear zone (Median Tectonic Line). Strike-slip events located close to the intersection of Hinagu and Futagawa fault zone are dipping slightly to east, while those in the southern area (Hinagu fault zone) are dipping to west. Most of events contain only minor CLVD component, which is statistically insignificant and can be related to the velocity model uncertainty. Nevertheless, two of the CMTs involve significantly large CLVD component (~30%), which may reflect complex rupture process. Decomposition of those moment tensors into two pure-shear moment tensors is non-unique. Nevertheless, preserving T-axis of the decomposed moment tensors suggests combined right-lateral strike-slip and dip-slip mechanisms, which are consistent with the tectonic settings of the intersection of the Hinagu and Futagawa fault zones. Finally, the Bayesian full-waveform inversion of CMTs of the Kumamoto earthquake sequence demonstrates the abilities of such a methodology, and suggests complex tectonic background for this earthquake sequence.