Is the Sangre de Cristo Fault in the Rio Grande Rift Reawakening?

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

In November of 2018, residents living near Great Sand Dunes National Park reported hearing and feeling multiple earthquakes, and reports of additional earthquakes have continued. These earthquakes occurred on or near the Sangre de Cristo Fault, a major west dipping normal fault within the Rio Grande Rift in south-central Colorado and north-central New Mexico. The fault is capable of generating earthquakes M7 or greater (McCalpin, 1982), but it has not ruptured with a large, damaging earthquake in historic times. This 250-km-long fault runs along the east side of the San Luis Valley at the base of the Sangre de Cristo Mountains. Based on geomorphic expression, the fault is subdivided into three sections (Ruleman and Machette, 2007): a northern section extends from near Poncha Pass to the base of Blanca Peak in Colorado; a central section continues southward to the Colorado-New Mexico state line; and a third section goes southward beyond Taos, New Mexico. McCalpin (1982, 2006) conducted paleoseismic investigations of the northern section, and Crone et al. (2006) studied the central section. These studies indicate that the rupture history of the fault is complex; that multiple late Quaternary ruptures characterize the fault, with slip rates ranging from ~0.06 to 0.2 mm/yr. Between 1970 and 2017, only three earthquakes were recorded by the USGS in the vicinity of the northern section of the fault. Using the earthquakes reported by local residents as templates, we form a subspace detector using data from a seismometer located at Great Sand Dunes National Park (US.SDCO, 12km away). We detect many small previously unreported earthquakes (~M 0.0+, up to 200 per day). Using all high signal-to-noise detected events, we form a detector and process the long-term continuous data at stations US.SDCO, TA.S22A, TA.T25A, and TA.Q24A. These newly detected events give new insight into the low-rate seismicity on the Sangre de Cristo fault.

Presenting Author: Jackson P. Bell

Authors