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Complex Multi-segment Rupture of the 2025 M 6.0 Afghanistan Earthquake From Sentinel-1 InSAR Data

Description: 

On 31 August 2025, a M 6.0 earthquake occurred in northeastern Afghanistan in the southern Pamir-Hindu Kush region. Afghanistan has limited local seismic network data and field access is limited, meaning that InSAR is likely. Despite its modest size, the earthquake had a significant impact resulting in ~2200 fatalities and major economic loss of over $100 million. It was also a complex event – estimates of the source time function from teleseismic data, as well as the InSAR deformation pattern, indicate that the rupture had multiple subevents. In this study, we use InSAR data from four Sentinel-1 tracks, processed using the ISCE software, to constrain and model the complex multi-segment rupture. To improve the coseismic signal and reduce unwrapping errors, we construct a preliminary model based on hand-digitized data to flatten the interferogram prior to unwrapping then manually correct for any phase jumps. We downsample the data using quadtree decomposition and model the fault geometry (e.g. fault length, fault width, slip) using a rectangular dislocation model (Okada, 1985) and determine the best-fitting parameters through nonlinear optimization (a Powell algorithm with multiple Monte Carlo restarts).

Our preliminary results suggest that the rupture involved near-simultaneous rupture of two faults a primary ENE-striking structure in the north and a secondary WSW-striking two segment structure located ~9 km to the southeast. Both faults exhibited inward-dipping oblique thrust faulting mechanisms with minor left-lateral strike-slip components, suggesting that the earthquake is accommodating regional tectonic compression. To best fit the observed data, we implement a three-segment fault model, with a bend in the secondary fault, which shows smaller residuals compared to a two-segment fault model. The northern fault is ~6.3 km long with uniform slip of 1.0 m, while the shallower secondary fault segment is ~3 km long with a slight change in strike with a uniform slip of ~1.3 m.

Session: SSJ-SSOC-SSA Joint Session: Lessons from Recent Major Earthquake Sequences Around the World - I

Type: Oral

Date: 4/17/2026

Presentation Time: 02:15 PM (local time)

Presenting Author: Karlee M. Rivera

Student Presenter: Yes

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