[S09P-05] Analysis of seismicity and crustal movement on the eastern side of Izu Peninsula
The Izu Peninsula in central Japan is in the northern most part of the Izu Bonin Mariana Arc and is located in the collision zone with Honshu Island, where crustal deformation is active. This Peninsula is volcanically and seismically active. The eastern side of the Izu Peninsula is a monogenic volcano field where volcanoes are included in the Izu-Tobu Volcano Group. This Volcano Group is listed as an active volcano where the Japan Meteorological Agency (JMA) operates 24-hours monitoring in a real-time manner. In a region along and off the east coast of the Izu Peninsula, which we called the Izu-Tobu region in this study, earthquake swarms of high-frequency and ordinary earthquakes frequently occur at shallow depths, which is considered to be associated with magma intrusion. Beneath ordinary earthquakes, low-frequency earthquakes (LFEs) are infrequently observed.
Here, we conducted a timeseries analysis of both types of earthquakes during the time period 2005-2020, using a variant of the Epidemic-Type Aftershock Sequence (ETAS) model. For this analysis, we used the JMA catalog of ordinary earthquakes and the catalog of LFEs produced using the matched filter method. The observed result, which was common to both types of earthquakes, showed a significant change in seismicity, which became quiet, with the inflection point falling sometime between late 2009 and mid-2013, during which two out of three pronounced earthquake swarms occurred. We associated this seismic quiescence with changes in background rate to be low, where background rate, by removing the triggering effect of aftershocks, was interpreted as having been caused directly by the magma source, which can vary with time.
We then used surface displacement data obtained from the Geospatial Information Authority of Japan, and observed that the uplift due to magma intrusion was significant during the 1970s-1990s whereas it was in abatement or unobservable during the studied period (2005-2020). We also found that the seismic quiescence occurred without significant crustal movement during the studied period. Our implication from this finding is that magma source, which caused magma intrusion into the Izu-Tobu region, is in a transition phase, becoming less active, compared with the magma source during the 1970s-1990s. We pointed out that this implication is consistent with the history of repeated uplift events obtained from morphological and stratigraphic survey conducted in and around the Izu-Tobu region.
Preprint associated partially with this presentation is available at https://doi.org/10.48550/arXiv.2407.19648 and http://ssrn.com/abstract=4921901.
Here, we conducted a timeseries analysis of both types of earthquakes during the time period 2005-2020, using a variant of the Epidemic-Type Aftershock Sequence (ETAS) model. For this analysis, we used the JMA catalog of ordinary earthquakes and the catalog of LFEs produced using the matched filter method. The observed result, which was common to both types of earthquakes, showed a significant change in seismicity, which became quiet, with the inflection point falling sometime between late 2009 and mid-2013, during which two out of three pronounced earthquake swarms occurred. We associated this seismic quiescence with changes in background rate to be low, where background rate, by removing the triggering effect of aftershocks, was interpreted as having been caused directly by the magma source, which can vary with time.
We then used surface displacement data obtained from the Geospatial Information Authority of Japan, and observed that the uplift due to magma intrusion was significant during the 1970s-1990s whereas it was in abatement or unobservable during the studied period (2005-2020). We also found that the seismic quiescence occurred without significant crustal movement during the studied period. Our implication from this finding is that magma source, which caused magma intrusion into the Izu-Tobu region, is in a transition phase, becoming less active, compared with the magma source during the 1970s-1990s. We pointed out that this implication is consistent with the history of repeated uplift events obtained from morphological and stratigraphic survey conducted in and around the Izu-Tobu region.
Preprint associated partially with this presentation is available at https://doi.org/10.48550/arXiv.2407.19648 and http://ssrn.com/abstract=4921901.