El Cuchillo Seismic Sequence of October 2013-July 2014 in the Burgos Basin, Northeastern Mexico: Hydraulic Fracturing or Reservoir-Induced Seismicity?

摘要

We studied the origin of the seismic sequence from October 2013 to July 2014 (2.8 = M = 4.5; hereafter the El Cuchillo seismic sequence) that shook the central part of the Nuevo Leon state in northeastern Mexico. This swarm has been quite controversial because its origin has been attributed to hydraulic fracturing by the press and social groups. Nowadays, there is a great interest in explaining the causes of this seismicity, as it was located in the Burgos basin (BB), an ideal province for shale gas production. We evaluated two possible anthropogenic-induced causes for this seismicity: (1) hydraulic fracturing to tight shale formations and (2) reservoir-associated seismicity by filling artificial water reservoirs. We did not find any correlation between fluid injection and seismicity, because: (1) there is no correlation in time, (2) most of the epicentral distributions are located beyond 5 km from the known wells, and (3) the hypocenter depths vary from 1 to 20 km, whereas the depths of the wells are less than 3.1 km For the reservoir-associated seismicity case, the b-value obtained from the Gutenberg-Richter relation is 1.08 +/- 0.1, which is correlated with several cases of dam-induced seismicity worldwide. The Pearson correlation obtained was 0.64, which outlines a positive linear relationship between the fluctuations of the water level and the El Cuchillo seismic sequence. The highest cross correlation derived (0.98) occurs relatively one month after the start of filling the reservoir, indicating a coincidence in time between the seismic activity and the fluctuations of the water level. Additionally, we estimated that pore pressures from the reservoir were approximately 100-250 kPa, adequate to induce M = 3.0 earthquakes in the area.