Earthquake Rupture and Tsunami Generation of the 2015 Mw 5.9 Bonin Event Revealed by In Situ Pressure Gauge Array Observations and Integrated Seismic and Tsunami Wave Simulation. Issue 22 (16th November 2021)

• Record Type: Journal Article
• Authors: Kubota, Tatsuya; Saito, Tatsuhiko; Fukao, Yoshio; Sugioka, Hiroko; Ito, Aki; Tonegawa, Takashi; Shiobara, Hajime; Yamashita, Mikiya
• Is Part Of: Geophysical research letters. Volume 48:Issue 22(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-16
• Subjects: in situ observation -- ocean‐bottom pressure gauge -- seafloor deformation -- seismic wave -- subduction -- tsunami; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL095915
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: On September 1, 2015, an M w 5.9 interplate earthquake occurred near the Bonin Trench. An array of in situ ocean‐bottom absolute pressure gauges (APGs) observed its tsunami generation field consisting of static and dynamic pressure changes due to tsunami and crustal deformation and due to seismic motion, respectively, under much higher station density than ever reported. We propose an approach to synthesize the pressure change inside the focal area, which reproduces the APG waveforms well. We further successfully estimate the finite fault model of the earthquake and constrain the rupture duration only from the APG data. The relatively low stress drop and seismic wave radiation from the fault model may suggest the nature of a tsunami earthquake. The in situ APGs have a large potential to reveal the broadband source process of the earthquake, which is essential to understand the seismotectonics in the subduction zone. Plain Language Summary: Absolute pressure gauges (APGs) installed on the seafloor have been widely used to observe various phenomena such as tsunamis. When an APG is located inside a subseafloor earthquake source region, the tsunami generation field is observed, which includes not only tsunamis but also dynamic pressure changes related to seafloor dynamic motion during the earthquake fault slip. This study analyzed densely distributed APG array data, which contained the tsunami generation field of a magnitude‐5.9 earthquake that happened near the Izu‐Bonin Trench on September 1, 2015. This observation was performed by APG stations at higher station density than any data ever reported. This study synthesized this APG array data using the theory for tsunami generation and propagation, and the result explained the data dramatically well. This indicates the validity of the tsunami generation theory for actual observation inside the earthquake source area. We also estimated the slip distribution across the fault of this earthquake, which could not previously be obtained. Our results indicate the combination of APG data obtained inside the focal area and the theory for tsunami generation and propagation is useful for extracting the detailed information on the earthquake rupture process. Key Points: We examined pressure changes inside the source region of the 2015 Bonin M w 5.9 EQ where long‐period seismic waves overlap with tsunamis A numerical simulation for a fluid‐elastic medium was conducted for the pressure change synthetics above the seafloor Analyzing both tsunamis and dynamic ground motions enabled us to estimate the stress drop and the rupture duration of the M w 5.9 event