This project will target naturally-occurring groundwater to define both spatial and temporal variability in He-CO2 characteristics at three seismically active regions of California. The three regions are the San Jacinto Fault (SJF), and the San Andreas Fault (SAF) - both in Central California (Hollister-Parkfield) and southern California (Coachella Valley). The areal extent of He-CO2 variations in the three regions will be mapped paying particular attention to localities close to known fault traces. The new instrument previously developed in this lab (SPARTAH) will be deployed at sites with a strong mantle volatile input (as recorded by the primordial isotope 3He). SPARTAH can provide a high-resolution temporal record (hours-to-days) of He-CO2 variations over extended periods (months-to-years).
The following hypotheses, central to understanding the relationship between dissolved volatiles, such as He and CO2, and the occurrence of seismicity in California, will be addressed:
1. Faults are the principal conduits to the surface for mantle-derived volatiles. Observed 3He/4He will be used to determine whether the faults act as high permeability pathways between the deep crust/uppermost mantle and the surface and, if so, to model their fluxes. In turn, this will allow evaluation of whether or not variations in fluxes correlate with regions of intense microseismicity (SJF), virtually no seismicity (southern SAF) and frequent-to-infrequent earthquakes (Hollister-Parkfield). 2. CO2 is the major volatile phase leading to super hydrostatic pressure at depth. Coupled CO2/3He and d13C variations will be used to resolve CO2 into mantle and crustal components. Major areas of mantle CO2 leakage will be determined and realistic estimates of permeability at depth will be derived. 3. Temporal variability characterizes the volatile record and is related to the occurrence of seismic activity. To date, there is little or no record of temporal variations in volatile fluxes in seismically-active regions. This deficiency will be addressed through deployment of the SPARTAH instrument which will enable targeting sections of the temporal record when there is (a) seismic activity - to gauge the response (if any) of the He and CO2 (isotopes and relative abundances), and (b) no evidence of any (major) seismic disturbance. These parts of the He-CO2 background record are essential to establish the temporal baseline value. The temporal record of He-CO2 variations will be compared with the occurrence of nonvolcanic tremor - associated with slip on the SAF - which occurs in bursts ranging in frequency from every few days to months. SPARAH is designed to sample groundwater at high pumping rates/pressures continuously so such events can be captured.
This project will liaise with the NSF-funded Center for Ocean Science Education Excellence - California (COSEE CA) to develop a plan to extend the impact of the research beyond the bounds of academia. COSEE CA and Scripps have developed a multi-faceted collaboration with the San Diego Unified School District to support their new, district-wide, high school Earth Sciences program. A key element of this collaboration is partnering to provide a combination of on-going professional development for district Earth Science teachers, many of whom are teaching outside their area of expertise, and robust connections to current research in Earth and Ocean sciences at Scripps. The project will sponsor a 1-day workshop for 15 teachers in support of the Scripps/SDUSD collaboration that combines presentation of basic information on California seismicity and local plate tectonics with a focused look at project results on assessing the relationship between earthquakes and geochemical signals in groundwater.
