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Rupture Directivity of Small Earthquakes in Southern Korean Peninsula

Description: 

Good knowledge of rupture directivity is crucial for both earthquake physics and seismic hazard mitigation. Analyzing bulk of small earthquakes may provide insights into the potential mechanism of rupture directivity, but such studies have been rare in stable continental regions. The Southern Korean Peninsula (SKP) hosts a dense network of seismic stations and hence provides opportunities of investigating the characteristics of earthquake rupture in the SCR. We analyze the rupture properties of 28 small (M_L 2.1 – 4.1) earthquakes in SKP since 2019, employing the empirical Green’s function method to calculate the relative source time functions (RSTFs). Adopting the line source model, we use Bayesian inference to invert key finite source properties – rupture direction, length, velocity, and degree of asymmetry. This approach allows us to elucidate the characteristics of earthquake rupture by explaining variations in RSTF durations concerning azimuths and ray takeoff angles, while robustly characterizing parameter uncertainties by considering data errors and trade-offs.

Our analysis reveals that a majority of events display asymmetrical rupture with a dominant direction in accordance with the nodal plane of focal mechanism, while a few events exhibit nearly symmetrical rupture. This implies that the rupture directivity may be relatively common for small earthquakes in SCRs, challenging the simplistic assumption of symmetrical circular rupture. We further revisit the 2020 Haenam earthquake sequence that exhibited unusual swarm-like behavior in the lower crust of southwestern SKP. Five M ≥ 2 events show diverse spectrum of rupture behaviors, ranging from bilateral to unilateral, with contrasting directions. However, we find that the largest event (M_L 3.1) ruptured away from other earlier events, implying that those earlier events may have influenced the rupture direction and extent of the largest event. This demonstrates that the detailed analysis of small event ruptures could enhance our understanding of earthquake sequences in the SKP.

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Min-Seong

Student Presenter: Yes

Invited Presentation: 

Authors