Seismic Activity and Risks in the Socorro Region
of Central New Mexico

October 6, 2009

by Jana Stankova-Pursley, Susan Bilek, Richard Aster
New Mexico Tech, Department of Earth and Environmental Science

New Mexico is a moderately seismically active region, with earthquakes occurring in most parts of the state. The Socorro area has been the most active earthquake region of New Mexico during at least the past 150 years. During the past 45 years, approximately 50% of the seismic energy generated by earthquakes in New Mexico has been released in a region centered near Socorro, encompassing only about 2% of the state's total land area. This relatively high rate of earthquake activity in the Socorro region is due to an inflating sill of molten rock (magma) that is roughly 1300 square miles in area and sits approximately 12 miles beneath the surface of the fault-bounded Rio Grande rift.

The largest earthquakes of record in this region occurred during an ongoing earthquake swarm in 1906, and the magnitudes of the two largest events were approximately 5.8. For comparison, the largest felt and heard event from the most recent swarm in this region (August 2009) was M 2.6.

Earthquake swarms, defined as a series of earthquakes recurring for days in nearly the same location within minutes of each other, are very common in this region. Historical accounts of these swarms date back to the 1860s, and they have been recorded on local seismic instruments since the early 1960s (Figure 1, blue stars, Sanford et al., 2002). The majority of the earthquakes in these swarms are shallow (3-8 miles beneath the surface), and relatively small (M < 1.0). These small earthquakes are not damaging; however, based on historic seismicity and geologic evidence, there is a chance for a larger, possibly damaging event in the future (Wong, 2009). According to the US Geological Survey, there is an 18% chance of a large earthquake (M > 6.0) in the Socorro region in the next 100 years.

References

Sanford, A. R., Lin, K., Tsai, I., and Jaksha, L. (2002), Earthquake catalogs for New Mexico and bordering areas: 1869-1998. NM Bureau of Geology and Mineral Resources, Circular 210.

Wong I. G. (2009), Earthquakes in New Mexico. New Mexico EARTH MATTERS, winter 2009, published by the NM Bureau of Geology and Mineral Resources.

www.ees.nmt.edu/Geop/NM_Seismology.html

Figure 1: Seismicity near Socorro, NM. Shown are locations of historic earthquakes (M ≥ 1.3) in this region from Sanford et al., 2002 (blue stars), and the earthquake activity since October 2008 (-1.5 < M < 2.7; purple stars). The symbol size reflects the earthquake magnitude. The solid line represents the approximate extent of the Socorro magma body. Also shows are the locations of stations currently operated by NMT as part of the Socorro Seismic Network (blue circles).