New Mexico Geological Society Annual Spring Meeting — Abstracts

From the first data recorded in the fall of 1973 to now, the Los Alamos Seismograph Network (LASN) has operated for almost 43 years. During that time LASN data have been used to locate more than 2,600 earthquakes in north-central New Mexico. The network was installed for seismic verification research and to monitor local earthquakes for the Los Alamos National Laboratory (LANL) Seismic Hazards Program. LASN once included as many as 22 stations spread over a geographic area of 150 km (N-S) by 350 km (E-W), but was downsized to cover only the local area around Los Alamos, roughly 15 km N-S by 15 km E-W, in the mid 1980s. Until 2010, LASN operated only 7 permanent stations. Over the last 6 years, 7 additional microseismic stations have been added, expanding both the spatial coverage and density, as well as utilizing state-of-the-art sensors and digital recording and telemetry technology. An additional digital broadband station is now being installed on LANL property. Currently, 6 of the 14 microseismic stations are old short-period, analog UHF-telemetered stations with 1-Hz geophones. The other 8 stations have digital broadband seismometers with spread-spectrum digital RF telemetry. In addition, a strong-motion vertical array of digital accelerometers was installed in a wellbore on LANL property. All but one station have 3-component (vertical, north-south and east-west) sensors. Also, three forensic strong-motion accelerometers (SMA) are operated at LANL facilities and more are planned. LASN is now capable of monitoring not only local tectonic earthquake activity, but also very small volcano-seismic events associated with the nearby Valles Caldera, due to installation of 3 broadband stations in and around the caldera. We will present a description of the current LASN station, instrumentation and telemetry configurations, as well as the data-acquisition and event-detection software structure used to record events in Earthworm.

More than 2,000 earthquakes were detected and located in north-central New Mexico during the first 11 years of LASN’s operation (1973 to 1984). With the subsequent downsizing of the network, about 1-2 earthquakes per month are detected and located within about 150 km radius of Los Alamos. Over 950 of these nearby earthquakes have been located from 1973 to present. We recently updated the LASN earthquake catalog for north-central New Mexico up through 2013 and most of 2014. This involved re-assessing numerous historic locations in the previous catalog. We are also looking at subsets of the catalog that represent earthquake swarms or clusters, as well as tiny events on the Valles Caldera’s ring fracture that were not detected before the caldera stations were installed. We will present the most recently updated map of north-central New Mexico seismicity based on these efforts. Many of the events detected by LASN do not appear in other catalogs because the majority of nearby earthquakes have magnitudes less than 1.5 and are not detected by other networks. Since 1973, there have been only a handful of events that were felt locally by Los Alamos residents.