Open AccessShallow soil CO 2 flow along the San Andreas and Calaveras Faults, California
Author(s) -
Lewicki J. L.,
Evans W. C.,
Hilley G. E.,
Sorey M. L.,
Rogie J. D.,
Brantley S. L.
Publication year - 2003
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002jb002141
Subject(s) - advection , context (archaeology) , soil gas , terrain , geology , fault (geology) , spatial variability , environmental science , hydrology (agriculture) , soil water , atmospheric sciences , soil science , seismology , paleontology , ecology , statistics , physics , mathematics , geotechnical engineering , biology , thermodynamics
We evaluate a comprehensive soil CO 2 survey along the San Andreas fault (SAF) in Parkfield, and the Calaveras fault (CF) in Hollister, California, in the context of spatial and temporal variability, origin, and transport of CO 2 in fractured terrain. CO 2 efflux was measured within grids with portable instrumentation and continuously with meteorological parameters at a fixed station, in both faulted and unfaulted areas. Spatial and temporal variability of surface CO 2 effluxes was observed to be higher at faulted SAF and CF sites, relative to comparable background areas. However, δ 13 C (−23.3 to −16.4‰) and Δ 14 C (75.5 to 94.4‰) values of soil CO 2 in both faulted and unfaulted areas are indicative of biogenic CO 2 , even though CO 2 effluxes in faulted areas reached values as high as 428 g m −2 d −1 . Profiles of soil CO 2 concentration as a function of depth were measured at multiple sites within SAF and CF grids and repeatedly at two locations at the SAF grid. Many of these profiles suggest a surprisingly high component of advective CO 2 flow. Spectral and correlation analysis of SAF CO 2 efflux and meteorological parameter time series indicates that effects of wind speed variations on atmospheric air flow though fractures modulate surface efflux of biogenic CO 2 . The resulting areal patterns in CO 2 effluxes could be erroneously attributed to a deep gas source in the absence of isotopic data, a problem that must be addressed in fault zone soil gas studies.