9:45 AM - 10:00 AM
[SSS08-04] Trends in Seismic Activity in the Noto Peninsula and Interpretation of Anomalous Activities in the Pre-M7.6 Period
Keywords:Earthquake swarm, background seismicity, ETAS model, Noto earthquake
The main points of this presentation are summarized into four points as follows. First, we detected a series of accelerated seismic swarm activation in the deep part of the seismic swarm initiation area in early 2022, then contrasted it with a simultaneous rapid increase in GNSS baseline distance. At this time large-scale fluid movement and slow slip were possibly initiated and continued.
Next, we discuss the correspondence of the stress changes as well as the changes in seismic activity in relation with the geodetic variations assuming a precursory slip in the deep extension of the fault model of the M6.5 earthquake. The ΔCFS pattern assuming the deep slip is consistent with the seismic quiescence of the northern area, with the increasing trend in the baseline distance change, and the eastward migration of the earthquake swarm in the southern area. These were all variations seen since the end of 2022. Similarly, the ΔCFS pattern, which assumes an afterslip of the M5.4 fault, is consistent with the seismic quiescence observed in the northern areas.
The M6.5 earthquake of May 2023 and its largest aftershock (M5.9) occurred in an area where the seismicity was sparse, and a number of foreshocks occurred in the vicinity of the main shock. In addition, the distribution of seismicity along the direction from M5.0, the largest aftershock immediately after the 2022 M5.4 event, to the M6.5 suggests fluid movement from deep to shallow areas and a slow slip.
Finally, regarding the activity after the M6.5 event, the analysis for 0.4 days after the main shock shows a quiescence in the surrounding area just before the maximum aftershock of M5.9. Longer-term non-stationary ETAS model analysis shows that the background intensity in the aftershock region decreased significantly after the M6.5 event and increased after a while.
In addition, trends and statistical characteristics of seismic activity after the M7.6 earthquake in 2024 will be discussed in a sequential update.
Next, we discuss the correspondence of the stress changes as well as the changes in seismic activity in relation with the geodetic variations assuming a precursory slip in the deep extension of the fault model of the M6.5 earthquake. The ΔCFS pattern assuming the deep slip is consistent with the seismic quiescence of the northern area, with the increasing trend in the baseline distance change, and the eastward migration of the earthquake swarm in the southern area. These were all variations seen since the end of 2022. Similarly, the ΔCFS pattern, which assumes an afterslip of the M5.4 fault, is consistent with the seismic quiescence observed in the northern areas.
The M6.5 earthquake of May 2023 and its largest aftershock (M5.9) occurred in an area where the seismicity was sparse, and a number of foreshocks occurred in the vicinity of the main shock. In addition, the distribution of seismicity along the direction from M5.0, the largest aftershock immediately after the 2022 M5.4 event, to the M6.5 suggests fluid movement from deep to shallow areas and a slow slip.
Finally, regarding the activity after the M6.5 event, the analysis for 0.4 days after the main shock shows a quiescence in the surrounding area just before the maximum aftershock of M5.9. Longer-term non-stationary ETAS model analysis shows that the background intensity in the aftershock region decreased significantly after the M6.5 event and increased after a while.
In addition, trends and statistical characteristics of seismic activity after the M7.6 earthquake in 2024 will be discussed in a sequential update.