The University of Tokyo · Earth and Planetary Sciences
Professor Osamu Sandanbata's research lab specializes in volcanic and tsunami hazard analysis, focusing on the seismic and geodetic mechanisms underlying submarine volcanic activity and associated tsunamis. The lab investigates complex source processes such as ring-faulting, trapdoor faulting, and magma-driven deformation using long-period seismic data, tsunami waveforms, and ocean-bottom pressure gauge observations. A key research direction involves quantifying the role of volcanic overpressure, fault geometry, and Earth's elastic and gravitational responses in generating moderate but hazardous tsunamis. The lab also explores the influence of physical factors like seawater compressibility and ocean stratification on tsunami propagation, particularly for long-period and trans-oceanic waves.
Figures are computed from collected data and may differ slightly.
Abstract Moderate earthquakes ( M w > 5) with moment tensors (MTs) dominated by a vertical compensated‐linear‐vector‐dipole (vertical‐CLVD) component are often generated by dip slip along a curved ring‐fault system at active volcanoes. However, relating their MTs to ring‐fault parameters has been proved difficult. The objective of this study is to find a robust way of estimating some ring‐fault parameters based on their MT solutions obtained from long‐period seismic records. We first model th
Abstract The main cause of tsunamis is large subduction zone earthquakes with seismic magnitudes M w > 7, but submarine volcanic processes can also generate tsunamis. At the submarine Sumisu caldera in the Izu–Bonin arc, moderate‐sized earthquakes with M w < 6 occur almost once a decade and cause meter‐scale tsunamis. The source mechanism of the volcanic earthquakes is poorly understood. Here we use tsunami and seismic data from the recent 2015 event to show that abrupt uplift of the subma
Abstract We observed the activity of long‐period tremors (LPTs) with a period of ~15 s at Aso volcano, Japan, during a 3 year period including the 2014 eruptions. The number of LPTs detected systematically increased 3 months before the Strombolian eruptions. LPT activity can be divided into five stages based on rapid changes in the maximum LPT amplitude. The amplitude‐frequency relation follows an exponential distribution during each stage before the Strombolian eruptions, with different charact
Abstract On 8 October 2023, mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events with body‐wave magnitudes m b 4–5 have been documented to the west of Sofugan volcano. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean bottom pressure gauges. Stacked waveforms of pressure gauge records suggest recurrent arrivals of multiple wave trains. Deconvolution of the stac
SUMMARY Tsunamis are often modelled as surface gravity waves of incompressible homogenous water propagating over a rigid seafloor. Previous studies have noted that when computing long-period tsunamis travelling at trans-oceanic distances with dominant periods of thousands of seconds, we need to consider four factors that are not included in the surface gravity wave theory: compressibility of seawater, density stratification of oceans, elasticity of the Earth and gravitational potential change as
Abstract Two submarine earthquakes ( M w 5.8) occurred near volcanic islands, Curtis and Cheeseman, in the Kermadec Arc in 2009 and 2017. Following both earthquakes, similar tsunamis with wave heights of about a meter, larger than expected from their moderate seismic magnitudes, were observed by coastal tide gauges. We investigate the source mechanism for both earthquakes by analyzing tsunami and seismic data of the 2017 event. Tsunami waveform analysis indicates that the earthquake uplifted a s
Abstract Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita‐Ioto Island, south of Japan, unusual M ∼ 5 non‐double‐couple volcanic earthquakes exhibited quasi‐regular recurrence near a submarine caldera. Following the earthquakes in 2008 and 2015, a distant ocean bottom pressure sensor recorded distinct tsunami signals. In this study, we aim to find a source model of the tsunami‐generating earthquak
<strong>Descriptions</strong> This dataset contains supplementary materials for the manuscript submitted to Journal of Geophysical Research: Solid Earth; the preprint has been uploaded to ESS Open Archive: Osamu Sandanbata, and Tatsuhiko Saito, Quantifying magma overpressure beneath a submarine caldera:<br> A mechanical modeling approach to tsunamigenic trapdoor faulting near Kita-Ioto Island, Japan. We present a mechanical source model for the 2008 Kita-Ioto caldera earthquake.
On 9 October 2023 (JST), mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events of body-wave magnitudes mb 4–5 have been documented in the southwest of Torishima Island. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean-bottom pressure gauges. A stacked waveform of 16 records suggests recurrent arrivals of multiple wave trains. Deconvolution of the stacked wavefo
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/10.102
The main cause of tsunamis is large subduction zone earthquakes with seismic magnitudes Mw > 7, but submarine volcanic processes can also generate tsunamis. At the submarine Sumisu caldera in the Izu–Bonin arc, moderate-sized earthquakes with Mw < 6 occur almost once a decade and cause meter-scale tsunamis. The source mechanism of the volcanic earthquakes is poorly understood. Here we use tsunami and seismic data for the recent 2015 event to show that abrupt uplift of the submarine caldera, with
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Solid Earth. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing an older version [v1]Go to new versionMoment tensors of ring-faulting at active volcanoes: Insights into vertical-CLVD earthquakes at the Sierra Negra caldera, Galápagos IslandsAuthor
Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita-Ioto Island, south of Japan, unusual M~5 non-double-couple volcanic earthquakes exhibited quasi-regular repetition near a submarine caldera. Following the 2008 earthquake, a distant ocean bottom pressure sensor recorded a distinct tsunami signal. In this study, we aim to find a source model of the tsunami-generating earthquake and quantify the pre-
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