Bibliographic Details
| Title: |
Segmented Trapdoor Fault in Kita‐Ioto Caldera, Japan: Insights From Millimeter Tsunami Waves Captured by an Array Network of Ocean Bottom Pressure Gauges. |
| Authors: |
Sandanbata, Osamu1,2,3 (AUTHOR) osm3@eri.u-tokyo.ac.jp, Saito, Tatsuhiko2 (AUTHOR) |
| Source: |
Journal of Geophysical Research. Solid Earth. Dec2024, Vol. 129 Issue 12, p1-23. 23p. |
| Subject Terms: |
*OCEAN bottom, *SUBMARINE volcanoes, *EARTHQUAKE magnitude, *PRESSURE gages, *CALDERAS, *TSUNAMIS, *SENDAI Earthquake, Japan, 2011 |
| Abstract: |
Submarine calderas with active magma supply have recently been identified as potential sources of volcanic tsunamis due to sudden meter‐scale uplift by trapdoor faulting, occurring every few years to a decade. These trapdoor uplifts are seismically recorded as non‐double‐couple earthquakes with magnitudes M > 5. Kita‐Ioto Caldera, a submarine caldera in the Izu‐Bonin arc, caused such earthquakes every 2–5 years. Our previous study (Sandanbata & Saito, 2024, https://doi.org/10.1029/2023jb027917) analyzed data from a single ocean bottom pressure (OBP) gauge in the Philippine Sea, confirming trapdoor uplifts during the earthquakes in 2008 and 2015. However, high temporal‐resolution data for the earthquakes in 2017 and 2019 were lost, preventing source mechanism investigation. To address this, we examine OBP data of the two recent earthquakes from the array network of Dense Oceanfloor Network system for Earthquakes and Tsunamis, deployed off the southwestern coast of Japan. Despite the poor signal‐to‐noise ratio in each record, we successfully detect clear tsunami signals associated with the earthquakes using a waveform stacking method, with sea‐surface wave amplitudes of only 1–2 mm. By analyzing the data, we propose source models that represent trapdoor uplifts in the submarine caldera and accurately reproduce the detected tsunami waveforms, confirming the recurrence of trapdoor uplifts. Notably, differences in the tsunami waveforms between the 2017 and 2019 earthquakes suggest that different segments of the intra‐caldera fault system were activated. This segmentation likely influences the recurrence characteristics of the inflation cycle in calderas, which would be a key to understanding the magma accumulation process and assessing the sizes and timings of future trapdoor uplifts. Plain Language Summary: Submarine calderas with active magma supply have recently been identified as potential sources of volcanic tsunamis due to sudden seafloor uplift, occurring every few years to a decade. Our previous study revealed that Kita‐Ioto Caldera, a submarine caldera in south Japan, caused such uplift events with moderate‐sized unusual earthquakes. Similar earthquakes were observed recently in 2017 and 2019, but their source mechanisms were not confirmed. To reveal the mechanisms, we examine ocean bottom pressure data from an array of sensors off southwestern Japan. Despite noisy data, we detect tiny but clear tsunami signals by utilizing the similarity of tsunami waveforms at nearby gauges. The analysis of the tsunami signals shows that submarine caldera uplift events occurred during both earthquakes, similar to past events. Moreover, we demonstrate systematic differences in the tsunami waveforms between the two events and prove that different parts of the fault system within the caldera were ruptured. The inferred complexity of the fault system within the caldera may be a key to understanding how the caldera repeatedly generates significant uplift events. Key Points: Kita‐Ioto Caldera, a submarine volcano in Japan, has recently caused Mw 5.2–5.3 non‐double‐couple earthquakes every 2–5 yearsStacking ocean bottom pressure data at ∼1,000 km from the source extracts ∼1‐mm tsunami signals due to the 2017 and 2019 earthquakesThe tsunami waveforms are distinctly different between the two earthquakes, suggesting the segmentation of the intra‐caldera fault system [ABSTRACT FROM AUTHOR] |
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