17:15 〜 18:45
[U15-P24] Seismic-wave Radiation Process of the 2024 Noto Peninsula Earthquake from Multi-frequency Teleseismic P-wave Back-projection
キーワード：能登半島、震源過程、高周波地震波、バックプロジェクション解析、遠地P波
A large devasting earthquake of Mj 7.6 occurred in the Noto peninsula, Japan, on January 1st, 2024, destroying and collapsing many buildings with over 240 casualties. Aftershock distribution indicates that the fault length reaches about 150 km, which can be more widespread compared to other equivalent-class inland earthquakes in Japan. Some results of source inversions suggested the fault rupture propagates toward both inland and offshore areas from the hypocenter in the northern tip of the Noto peninsula. The relationship of this earthquake with the preceding seismic swarms, which have continued since 2020, has also been suggested. In this study, we investigate frequency-dependent seismic-wave radiation processes based on the back-projection (BP) of teleseismic P-waves for multiple frequency ranges (0.03-0.3 Hz; 0.05-0.5 Hz; 0.1-1.0 Hz; 0.25-1.75 Hz). From the time series of BP images for different frequency ranges, we discuss a plausible relation between high-frequency seismic wave radiation and the large-scale rupture process characterized by lower-frequency radiation of P-wave.
We employed teleseismic broadband waveform data from the Global Seismographic Network provided by the IRIS Data Management Center. After correcting the instrument responses, we selected coherent P waveforms based on cross-correlation analysis and slant-stacked them to reconstruct the BP images in the source locations. The BP analysis has successfully imaged the frequency-dependent P-wave radiation processes in the source area. The P-wave radiation lasted about 42 seconds from the origin time at 16:10:10 JST, which can be divided into four episodes: [E1] Initial radiation around the hypocenter (0-15 s), [E2] intense radiation in the inland of Noto peninsula (25-42 s), [E3] eastern offshore radiation (25-38 s), and [E4] rupture termination and high-frequency radiation (38-40 s). The main characters of each episode can be summarized as follows;
[E1]: P-wave radiation is dominated in the intermediate frequency range (0.05-1.0 Hz) near the hypocenter in the northern tip of the Noto peninsula.
[E2]: Significant low-frequency radiation (0.03-0.3 Hz) migrates toward the southwest inland areas of the Noto peninsula from 25 to 42 s, which may have contributed to the destructive damage of inland regions.
[E3]: The P-wave radiation area extends to the northeast offshore region from 25 to 38 s.
[E4]: The intense radiation processes of E2 and E3 rapidly cease in both western inland and eastern offshore areas at 40 s and 38 s, respectively. The abrupt cessation of P-wave radiation at lower frequency ranges (0.03-0.3Hz, 0.05-0.5Hz) reflects the rapid deceleration of fault slip at both eastern and western segments, which can be seen in the powerful P-wave radiation at the higher frequency range (0.25-1.75 Hz).
The complex fault rupture and seismic radiation processes imaged by our BP analysis may provide a key to understanding the relationship between this earthquake and seismic swarms that can be driven by crustal fluids.
We employed teleseismic broadband waveform data from the Global Seismographic Network provided by the IRIS Data Management Center. After correcting the instrument responses, we selected coherent P waveforms based on cross-correlation analysis and slant-stacked them to reconstruct the BP images in the source locations. The BP analysis has successfully imaged the frequency-dependent P-wave radiation processes in the source area. The P-wave radiation lasted about 42 seconds from the origin time at 16:10:10 JST, which can be divided into four episodes: [E1] Initial radiation around the hypocenter (0-15 s), [E2] intense radiation in the inland of Noto peninsula (25-42 s), [E3] eastern offshore radiation (25-38 s), and [E4] rupture termination and high-frequency radiation (38-40 s). The main characters of each episode can be summarized as follows;
[E1]: P-wave radiation is dominated in the intermediate frequency range (0.05-1.0 Hz) near the hypocenter in the northern tip of the Noto peninsula.
[E2]: Significant low-frequency radiation (0.03-0.3 Hz) migrates toward the southwest inland areas of the Noto peninsula from 25 to 42 s, which may have contributed to the destructive damage of inland regions.
[E3]: The P-wave radiation area extends to the northeast offshore region from 25 to 38 s.
[E4]: The intense radiation processes of E2 and E3 rapidly cease in both western inland and eastern offshore areas at 40 s and 38 s, respectively. The abrupt cessation of P-wave radiation at lower frequency ranges (0.03-0.3Hz, 0.05-0.5Hz) reflects the rapid deceleration of fault slip at both eastern and western segments, which can be seen in the powerful P-wave radiation at the higher frequency range (0.25-1.75 Hz).
The complex fault rupture and seismic radiation processes imaged by our BP analysis may provide a key to understanding the relationship between this earthquake and seismic swarms that can be driven by crustal fluids.