HR: 17:45h
AN: S12E-07    [PDF]
TI: Is Microseismicity Relevant to Estimating Seismic Hazards in North Central New Mexico?
AU: * House, L
EM: house@lanl.gov
AF: Los Alamos National Laboratory, MS D443, Los Alamos, NM 87545 United States
AU: Roberts, P
EM: proberts@lanl.gov
AF: Los Alamos National Laboratory, MS D443, Los Alamos, NM 87545 United States
AU: Gardner, J N
EM: jgardner@lanl.gov
AF: Los Alamos National Laboratory, MS D462, Los Alamos, NM 87545 United States
AB: The Rio Grande rift extends south from southern Colorado through central New Mexico and into northern Mexico. It is a major tectonic feature in New Mexico, yet seismicity in the rift is comparable to or lower than in the adjacent stable Great Plains and Colorado Plateau provinces (Sanford, et al, 1991). In north-central New Mexico, thirty years of microearthquake monitoring have provided more than 650 epicenters in an area of about 28 000 sq km. The largest earthquake was about magnitude 3. Epicenters show only a slight association with recently active faults, and most lie away from faults (mislocation of epicenters could produce this scatter, though we think it is unlikely). The Pajarito fault system is presently the western boundary of the Rio Grande rift in the area of the Espanola Basin (from Santa Fe to Espanola), yet has little seismicity associated with it, and only for 15 km of its 50 km length. That seismicity includes five earthquakes that were been felt in the Los Alamos area since 1991 (most recently in April 2003). Paleoseismic studies (Gardner et al, 2001) found evidence for large slip events along that same 15 km portion of the Pajarito fault system as recently as 2 ka. Recurrence times of these events are not known, but may be 10 ka or longer. The remainder of the rift boundary in north-central New Mexico is not discernable from seismicity. A simple model of opening of the rift (at an assumed rate of 0.1 mm/yr) produces an estimate of seismic moment release that is several orders of magnitude greater than seen in the seismicity. Microseismicity seems to have little relation to the macroseismicity that may occur on long time intervals (perhaps thousands of years) and may not be relevant for understanding seismic hazards in this part of the Rio Grande rift. Sanford, A.R., L.H. Jaksha, and D.J. Cash (1991), Seismicity of the Rio Grande rift in New Mexico, in Slemmons, D.B., E.R. Engdahl, M.D. Zoback, and D.D. Blackwell (eds), Neotectonics of North America, Geological Society of America, Boulder, CO. Gardner, J.N., S.L. Reneau, C.J. Lewis, A. Lavine, D. Katzman, L. Goodwin, J. Wilson, and K.I. Kelson (2001), Paleoseismic trenching in the Pajarito Fault system, Rio Grande rift, New Mexico, EOS (Trans. AGU), 82(47) Fall Meet. Suppl., Abstract S52C-0643.
DE: 7205 Continental crust (1242)
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting