Detecting and Analyzing the Displacement of a Small-Magnitude Earthquake Cluster in Rong County, China by the GACOS Based InSAR Technology

A series of small-magnitude earthquakes (Mw 2.9~Mw 4.9) occurred in Rong County, Sichuan Province, China between 30 March 2018 and December 2020, which threatened the safety of local residents. Determining the surface displacement and estimating the damage caused by these earthquakes are significant for earthquake relief, post-earthquake disaster assessment and hazard elimination. This paper integrates the Generic Atmospheric Correction Online Service (GACOS) with interferometry synthetic aperture radar (InSAR) to accurately detect the displacement of the series of small-magnitude earthquakes in Rong County based on 45 Sentinel-1 ascending/descending images acquired from January 2018 to December 2020. We analyze the influence of some factors involved in surface displacement, including earthquake magnitude, focal depth and the distance from the epicenter to the fault. The above measurement for small-magnitude earthquakes and statistics analysis for the displacement have not been performed before, so this can help better understand the displacement features of small-magnitude earthquakes, which are important for post-earthquake hazard assessment and disaster prevention.

Earthquake Cluster Analysis with Nearest Neighbor Approach in Taiwan

<p>Spatiotemporal evolution of earthquake clusters can give insights into fault geometry, triggering process, and potential interaction with fluid and heat. Taiwan is one of the most active orogenic belts with high deformation rate and complex crustal structures, so it is expected to observe seismicity driven by varying mechanisms among different geological processes. For investigating the tectonic complexity and the triggering processes of seismicity in Taiwan, a high-quality and robust catalog of earthquake clusters is critical. This study collected a long-term-effort earthquake catalog from the Central Weather Bureau from 1990/01 to 2018/06 and produced the earthquake cluster and background seismicity catalogs by four different declustering methods. Among which, the statistics-based nearest neighbor approach (NNA) performs most desirably for passing the Poisson process statistic tests while also remaining more events. We further classified the extracted earthquake clusters into the typical mainshock-aftershock (M-A) sequences and the swarms. Most of the M-A sequences are distributed near the Western Foothill. The asperity sizes, duration, and cluster event numbers all show positive correlations with mainshock magnitude. In contrast, the swarms are mainly distributed in the northern and southern Central Range and the northern Hualien regions. The lower correlation of the asperity sizes, duration, and swarm event numbers with the mainshock magnitude is showed in swarms. Moreover, we find that some of the swarm may be driven by fluid diffusion and spatial correlated with the high heat flow and spring regions.</p>

Comprehensive analysis of the March 7, 2019 Somogyszob, Hungary earthquake cluster

<div>A magnitude ML 4.0 earthquake struck southwest Hungary on March 7, 2019. The earthquake was reported to be felt in some 53 localities with maximum intensity V on the EMS scale. The earthquake was preceded by four foreshocks and followed by four aftershocks. The hypoDD solutions using differential travel times from waveform cross-correlation show significant improvements in event location. We were able to determine the moment tensor solutions for the main shock and one of the foreshocks and aftershocks, each representing thrust fault mechanism with a horizontal P-axis pointing towards N-NE. The obtained moment magnitudes range from Mw 1.5 to 3.8 with source radii between 100 and 500 m. The stress drop spans from 12 to 19 bars.</div><div> <div> <div> </div> </div> </div>