Seismicity of Eagle Ford Since the Implementation of TexNet Earthquake Catalog January 1, 2017
From January 2017 through September 2018, TexNet located 132 earthquakes of ML 1.1 to ML 3.5. This includes 6 events ML ≥ 3.0, 64 events 3.0 > ML ≥ 2.0, and 67 events ML < 2.0. The majority of these earthquakes took place south-southeast of San Antonio in an arc from Atascosa to Gonzales counties. Eleven events, southeast from San Antonio, had sufficient low signal to noise ratio (SNR) for focal mechanism calculations. The eleven events are normal faults with strike trending in the southwest to northeast direction, parallel to the Gulf of Mexico coast. This corresponds with known fault geometry of the area, normal fault dipping to the southeast.
Late May through early June 2018, there was a cluster of 17 earthquakes south from San Antonio in the Atascosa county. Events range in magnitude ML 1.4 to ML 3.1. The ML 3.1 on June 1 had low enough SNR to calculate a focal mechanism, a normal fault with strike trending in the southwest to northeast direction. This area currently has no known mapped quaternary faults. TexNet recorded one other earthquake in this area on July 2, 2017 with an ML 2.0. These events take place in the Eagle Ford Shale. The Mw 4.8 20 October 2011 earthquake, near Fashing, Texas, followed similar fault geometry (Frohlich and Brunt, 2013) denoting also the main strike directions of fault zones in the Eagle Ford play.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019