Evidence for Long-Time Scale ( > 103 years) Changes in Hydrothermal Activity Induced By Seismic Events

Wednesday, 17 December 2014: 11:35 AM
Mark Austin Person1, Trevor Howald1, Andrew Campbell1, Albert Hofstra2, Virgil Leuth1, Donald Steven Sweetkind3, Carl W Gable4, Elco Luijendijk5, Laura J Crossey6, Karl E Karlstrom6, Shari Kelley7 and Fred M Phillips8, (1)NM Tech, Socorro, NM, United States, (2)USGS Central Region Office, Lakewood, CO, United States, (3)USGS, Denver, CO, United States, (4)Los Alamos National Laboratory, Los Alamos, NM, United States, (5)Georg-August-Universitaet Goettingen, Goettingen, Germany, (6)University of New Mexico Main Campus, Albuquerque, NM, United States, (7)New Mexico Bureau of Geology and Mineral Resources, Socorro, NM, United States, (8)New Mexico Institute of Mining and Technology, Socorro, NM, United States
The pollen 14C age and oxygen isotopic composition of siliceous sinter deposits from the former Beowawe geyser field reveal evidence of two hydrothermal discharge events that followed relatively low-magnitude ( < M5) earthquakes of Holocene and Late Pleistocene age along the Malpais fault zone in Whirlwind Valley, Nevada, USA. The observed 20 %o trend of decreasing over about a 5000 to 7000 year period following each earthquake is consistent with a single-pass, fault-controlled groundwater flow system that received increasing amounts of recharge of cool, unexchanged, meteoric water through time. Hydrothermal/isotopic model reconstructions of the Beowawe system suggests that each of the earthquakes must have produced at least a 103 fold increase in fault permeability (from < 10-14 m2 to > 10-11 m2). Observed overturned temperature profiles in geothermal wells close (300m) to the Malpais fault suggest the onset of thermal convection occurred over shorter time scales (200-1000 years). We suggest that individual Malpais fault segments become clogged on shorter time scales and new routes to the surface are taken.