Seismicity at the northeast edge of the Mexican Volcanic Belt (MVB) and activation of an undocumented fault: the Peñamiller earthquake sequence of 2010–2011, Querétaro, Mexico

Abstract

Abstract. The town of Peñamiller in the state of Querétaro, Mexico, is located at the northeast border of the seismogenic zone known as the Mexican Volcanic Belt (MVB), which transects the central part of Mexico with an east–west orientation. In the vicinity of this town, a sequence of small earthquakes occurred during the end of 2010 and beginning of 2011. Seismicity in the continental regimen of central Mexico is not too frequent; however, it is known that there are precedents of large earthquakes (Mw magnitude greater than 6.0) occurring in this zone. Three large earthquakes have occurred in the past 100 yr: the 19 November 1912 (MS = 7.0), the 3 January 1920 (MS = 6.4), and the 29 June 1935 (MS = 6.9) earthquakes. Prior to the instrumental period, the earthquake of 11 February 1875, which took place near the city of Guadalajara, caused widespread damage. The purpose of this article is to contribute to the available seismic information of this region. This will help advance our understanding of the tectonic situation of the central Mexico MVB region. Twenty-four shallow earthquakes of the Peñamiller seismic sequence of 2011 were recorded by a temporary accelerograph network installed by the Universidad Autónoma de Querétaro (UAQ). The data were analyzed in order to determine the source locations and to estimate the source parameters. The study was carried out through an inversion process and by spectral analysis. The results show that the largest earthquake occurred on 8 February 2011 at 19:53:48.6 UTC, had a moment magnitude Mw = 3.5, and was located at latitude 21.039° and longitude −99.752°, at a depth of 5.6 km. This location is less than 7 km away in a south-east direction from downtown Peñamiller. The focal mechanisms are mostly normal faults with small lateral components. These focal mechanisms are consistent with the extensional regimen of the southern extension of the Basin and Range (BR) province. The source area of the largest event was estimated to have a radius of 0.5 km, which corresponds to a normal fault with azimuth of 174° and an almost pure dip slip. Peak ground acceleration (PGA) was close to 100 cm s−2 in the horizontal direction. Shallow earthquakes induced by crustal faulting present a potential seismic risk and hazard within the MVB, considering the population growth. Thus, the necessity to enrich seismic information in this zone is very important since the risk at most urban sites in the region might even be greater than that posed by subduction earthquakes.

Comment on “Active Crustal Deformation in the Trans‐Mexican Volcanic Belt as Evidenced by Historical Earthquakes During the Last 450 Years” by G. Suárez et al.

“…A north-south striking normal fault northwest of Pinal de Amoles with a morphologically pronounced fault scarp, 45 km long, likely was the source of the 1887 event (Suter et al, 1996, their Figure 2). An earthquake sequence in 2010-2011, located just south of the trace of this fault, yielded focal mechanisms indicating a north-south striking normal fault as source (Clemente-Chávez et al, 2013). The northern margin of the TMVB is located~60 km south of Pinal de Amoles, where north striking normal faults of the Basin and Range Province are intersected by east-west striking normal faults of the Aljibes half-graben (Suter et al, 1995).…”