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Fault Geometries of the 2024 Mw 7.5 Noto Peninsula Earthquake From Hypocenter Clustering

Description: 

Understanding intricate fault geometries is crucial for seismology. The New Year’s Day 2024 earthquake at the Noto Peninsula in central Japan, with a Mw of 7.5, was one of Japan’s largest reverse-fault crustal earthquakes. The aftershocks extended over 150 km from the western region to the northeastern offshore. As hypocenter alignments typically reflect complex crustal fault structures, we developed a hypocenter clustering method to objectively extract intricate fault geometries of the Noto Peninsula earthquake, integrating point-cloud normal vectors (PCNVs) that reflect the local surface geometry of a point of interest.

For hypocenter clustering, we relocated 14,395 events in January 2024 using tomoDD under the fixed 3-D velocity model (Nakajima, 2022). PCNVs were estimated from the distribution of surrounding points, and HDBSCAN (Campello et al., 2013) was used for clustering hypocenter locations and PCNVs.

Our analysis extracted five planes beneath the peninsula, each 10–20 km in length. These included ENE-striking faults along the northern coast and a north-striking east-dipping fault in the southwestern area. Notably, the fault planes aligned with coastal lines from the western to northern coast. Additionally, we extracted an NE-striking plane in eastern Wajima between two ENE-striking planes in the northern coast, correlating with the gravity anomaly and surface geology, highlighting the complexity of fault ruptures.

Furthermore, the east-dipping fault in the western area was consistent with NS-trending aftershock focal mechanisms. NS-trending reverse-fault slip may be key to understanding seismotectonics of the Noto Peninsula.

[Acknowledgments]

This study was supported by MEXT Project for Seismology toward Research Innovation with Data of Earthquake (STAR-E) Grant Number JPJ010217.

Session: Building and Decoding High-resolution Earthquake Catalogs With Statistical and Machine-learning Tools - I

Type: Oral

Date: 4/15/2025

Presentation Time: 05:00 PM (local time)

Presenting Author: Takahiko

Student Presenter: No

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