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Source Characterization of Complex Earthquakes via Subevent Decomposition: Application to Apparent-repeating Earthquakes

Description: 

Stress drops of small earthquakes are often estimated under the assumption of a simple rupture process. However, some real rupture processes exhibit significant complexities, with multiple shocks being one example. Repeating earthquakes are considered to result from intermittent seismic slip on isolated earthquake patches and are generally assumed to involve a simple rupture process. However, it is also known that they can exhibit complex behaviors, such as magnitude variations, especially after large earthquakes. Advancing the understanding of these rupture processes is crucial for improving insights into the earthquake propagation process. We investigated the characteristics of the rupture processes for several sequences of repeating earthquakes along the Japan Trench that exhibited significant magnitude variations.

The sequence introduced here consists of approximately 50 earthquakes with magnitudes varying between Mw ​3 and 4. By performing deconvolution using the waveforms of a nearby smaller earthquake, the apparent moment-rate function (AMRF) was estimated. The results show that events with Mw​ <3.6 exhibited a single-pulse rupture, while those with Mw​ >3.6 generated an additional rupture. Depending on the loading rate, the final magnitude, slip amount, and the number of patches appear to vary.

Rupture separation was performed using Kikuchi & Kanamori's (1982) method, placing candidate sources on a planar fault consistent with the plate boundary. This approach determined the locations, onset times of up to two sources, and a common duration. Based on the obtained duration and seismic moment, stress drops for each patch were estimated using Brune's (1970) model, ranging from 20 to 50 MPa. These values exceed typical estimates for small earthquakes in Japan but align well with Nadeau & Johnson's (1998) empirical relationship for this magnitude range. If the stress drop were around 3 MPa, the patches would become too large and overlap significantly, suggesting the targeted downdip repeating earthquakes may genuinely have high stress drops.

Session: Advances in Reliable Earthquake Source Parameter Estimation [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Keisuke

Student Presenter: No

Invited Presentation: 

Poster Number: 38

Authors