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Multiscale 3D View of Faults Activated in the 3 April 2024 Hualien Taiwan Earthquake Sequence, Illuminating the Walls of a Giant Subduction Channel and the Orthogonal Juncture of Two Subduction Systems

Description: 

The shallow 3 April 2024 M~7.4 Hualien earthquake sequence took place precisely at the orthogonal juncture of the Ryukyu and Luzon Manila Trench subduction systems at the northeastern coast of Taiwan, activating major interfaces of both systems, including faults of the Ryukyu subduction channel and the Luzon forearc subduction interface of the Manila system. We integrate multiscale data in 3D in Aspentech Gocad software, including local tomographies, previous seismicity, previous multi-scale focal-mechanism stress inversion, marine seismic reflection data, offshore bathymetry and fault mapping (Y-H Hsieh, this meeting), April 2024 aftershock locations and mechanisms (CWB and BATS), and finite fault models (Shiann-Jong Lee, IES). We had mapped faults in 3D after the 2013 Ruisui and 2018 Hualien earthquakes using high resolution local tomography and relocated seismicity. These fault models fit the April 2024 aftershocks well, and we are refining them with 2024 data. The 2024 mainshock hypocenter and many aftershocks fit well with the mapped forearc subduction interface from ~45km depth up to its intersection with a west-dipping fault that projects eastward to the surface trace of the Takangko High thrust (Y-H Hsieh et al. 2020; fault 22 of the TEC Taiwan Fault Model of Bruce Shyu). The high-slip portion of the 3 April 2024 mainshock is confined to a 15 km x 30 km geometric segment of this fault, as shown by projecting the west-dipping finite-fault model of Shiann-Jong Lee (IES) onto our pre-earthquake fault model. The Takangko High fault is the shallow up-dip portion of a regional ~110km long west-dipping fault that we have informally called the Suao-Hualien-Ruisui fault that activated in the 2013 Ruisui earthquake. At the northern end of the 2024 sequence this fault turns eastward to become the roof-thrust of the Ryukyu subduction channel. The floor thrust, which is the main detachment of both the Ryukyu accretionary wedge and the offshore eastern Taiwan thrust belt (Y-H Hsieh et al. 2020), was illuminated by aftershocks of the April 2024 sequence.

Session: The 3 April 2024 Magnitude 7.4 and 6.4 Earthquakes and Aftershock Sequence Near Hualien City, Eastern Taiwan - I

Type: Oral

Date: 5/3/2024

Presentation Time: 11:15 AM (local time)

Presenting Author: John

Student Presenter: No

Invited Presentation: 

Authors