HR: 1330h
AN: ED42A-1201    [PDF]
TI: Radon Outgassing Along the Northern Calaveras Fault, California
AU: * Ararso, I
EM: pilotiskander16@yahoo.com
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Holtmann-Rice, D
EM: flyingtabmow@comcast.net
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Chan, T
EM: kcuff@uclink4.berkeley.edu
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Adarkwah, N
EM: kcuff@uclink4.berkeley.edu
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Louie, J
EM: kcuff@uclink4.berkeley.edu
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Ramanan, S
EM: csheelar@uclink.berkeley.edu
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Swami, V
EM: vijay_swamy_89@yahoo.com
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AU: Cuff, K
EM: kcuff@uclink4.berkeley.edu
AF: Lawrence Hall of Science, University of California, Berkeley, CA 94720
AB: The Calaveras fault is an active fault located near or within several major urban areas. A total of 26 earthquakes greater than magnitude M5.0 have occurred on the Calaveras fault since the mid-1800's. In an attempt to provide information that can be used to better understand the structure of the Northern Calaveras fault, we set out to conduct a radon outgassing survey of a small portion of the fault in San Ramon Valley. We measured soil-gas radon concentrations at 77 separate sites within a 70 by 110 meter grid, using detectors that were placed 10 meters apart. The long axis of the grid was east-west aligned, while the shorter axis had a north-south trend. Survey transects with this north-south trend spanned a depressed area believed to have formed as the result of faulting in the area. In addition, a fence exists at the southern-most edge of the grid, which has clearly been offset due to faulting. Based on the relatively young age of this fence, faulting in the survey area has occurred within the past 20 years. Following analysis of detectors used in this survey, a radon outgassing map was produced by plotting measured radon concentration values versus geographic coordinates. Analysis of this map indicated two significant features: parallel sets of northwest-southeast trending high values; and perpendicular sets of northeast-southwest trending high values. Each of these features contained individual values that were greater than four times background radon concentration levels measured in the field. The observed zones of anomalously high values are believed to be an indication of crisscrossing fractures underlying our survey area. The northwest-southeast fractures correspond nicely to the northwest-southeast alignment of previously mapped sections of the Calaveras fault, while the northeast-southwest fractures, known faults in the area, are associated with an unmapped, transform feature that is roughly perpendicular to the main fault trend. This is not surprising considering seismic data that shows numerous earthquake clusters occurring in northeast-southwest trend patterns along various sections of the Calaveras fault. At points within the survey area located above intersections of a northwest-southeast and northeast-southwest trending fractures, the highest radon outgassing values were observed. In some cases measured values were observed to be as much as three standard deviations from the mean of our entire data set.
DE: 6005 Atmospheres--composition and chemistry
SC: Education and Human Resources [ED]
MN: 2003 Fall Meeting