SEMINAR - Daniel Brothers

Imaging the fault structure and earthquake history beneath the Salton Sea

Daniel S. Brothers
Scripps Institution of Oceanography
Institute of Geophysics and Planetary Physics
University of California, San Diego

April 30th, 2008

The Salton Sea, California, covers an important section of the plate boundary where the Gulf of California ridge-transform system to the south transitions into the San Andreas strike-slip system to the north. However, this transition zone is poorly understood due to an absence of detailed geological and geophysical data beneath the Sea. To constrain deformation models and seismic hazards in this region we need to define the location, kinematics and rupture history of faults beneath the Sea and determine how these structures affect stress conditions along major faults in the region, such as the San Andreas and San Jacinto.

High-resolution seismic reflection data collected in 2006 and 2007 provide the first regional-scale imagery of faulting and stratigraphy beneath the Salton Sea. Seismic profiles reveal structural features that were previously unknown, including the continuation of the Extra Fault Zone (EFZ) between the San Felipe Hills and Durmid Hill, as well as several faults and seafloor scarps in the Brawley Seismic Zone. By correlating acoustic marker beds in the seismic data with stratigraphy documented in paleoseismic trenches onshore, we are able to constrain both the depositional history and the timing of past earthquakes beneath the Sea.

Thesis Defense - Spring 2008 - Adam Cosentino

Detrital zircon U-Pb geochronology of Paleozoic prebatholithic rocks in the northeastern Peninsular Ranges of Southern and Baja California

Adam Cosentino
M.S. Candidate
Department of Geological Sciences
San Diego State University

Friday, April 25th

ABSTRACT
In the northern Peninsular Ranges of southern and Baja California carbonate - quartzite dominated prebatholithic assemblages display lithologic similarities to in-situ cratonic North American miogeoclinal sequences. Correlation of the Peninsular Ranges rocks to the miogeocline and offshore equivalents however has proven difficult due to pervasive metamorphism and structural disruption associated with Cretaceous batholith emplacement. This study utilizes detrital zircon laser ablation ICPMS U-Pb ages to constrain the provenance and age of the Peninsular Ranges assemblages and make regional stratigraphic correlations in insitu North American rocks.
This study is focused on two main stratigraphic packages that represent the thickest and most complete prebatholithic assemblages within this ~350 km-long carbonate - quartzite belt: the Desert Divide Group (DDG) in the north and the Playa San Felipe Group (PSFG) in the south. The DDG at the northern end of the belt is divided into the structurally lower Bull Canyon Formation, comprised of schist, carbonate, and quartzite, and the structurally higher Ken Quartzite, an ~ 700 m thick package of relatively pure quartzite. Upper amphibolite metamorphism has obliterated fossils and sedimentary structures and the relationship between the Bull Canyon Fm and Ken Quartzite has remained uncertain. Detrital zircon U-Pb ages from closely spaced samples within an ~250 m thick section across the Bull Canyon-Ken Quartzite contact record a shift in provenance that matches closely a major Middle Ordovician regional detrital zircon provenance shift associated with the onset of “Peace River Arch” detritus. This shift is documented widely throughout the Cordilleran miogeocline (associated with the Eureka Quartzite) and the timing of the shift is so far best documented from the Vinini Formation where it occurs in the mid to late Middle Ordovician.
Detrital zircon U-Pb age spectra from PSFG Unit G quartzite (~430 m thick) yield a post shift, Peace River Arch signature which verifies previous detrital zircon studies on this unit. The close match of Unit G and the Ken Quartzite zircon spectra suggests these are correlative units. It also raises the possibility that the detrital zircon shift from the Bull Canyon to the Ken Quartzite in the DGG may be present in the PSFG.
Results from PSFG Unit A quartzite yield a maximum depositional age of Late Devonian based on 3 concordant grains at ~376 Ma. This result suggests that there are much younger Paleozoic stratigraphic elements in the PSFG than has been previously recognized as well as unrecognized structural complications in the area. The Unit A rocks may have correlatives in late Paleozoic sequences documented from the Sierra Las Pintas area ~85 km to the north.
Detrital zircon ages were also determined from an olistolith quartzite block deposited into early Mesozoic prebatholithic flysch near Rancho San Marcos in northern Baja California. The quartzite here is associated with carbonates that have yielded late Early Ordovician conodonts; this sample yields a “pre-shift” detrital zircon spectra consistent with the fossil age call.

SEMINAR - Wesley Danskin

Real-time Ground-water Management in San Diego




Wesley R. Danskin
Research Hydrologist
U.S. Geological Survey




April 23rd, 2008

• Advances in real-time monitoring of ground-water systems have improved the ability of local water managers to make timely decisions regarding recharge and pumpage. The goal is to avoid expensive problems, improve knowledge of the local aquifer, and to provide managers with real-time ground-water levels. Data are collected from each transducer every 15 minutes, and are transmitted via the satellite to the database every four hours. This easy access to real-time data from wells located three-dimensionally throughout the aquifer help enable water managers to make informed decisions regarding how much water to import from northern California, where to discharge imported water for artificial recharge, and how much and where to pump ground water for municipal supply.

Professional Expertise:

• Optimal water management
• Ground-water simulation, constrained optimization
• Hydrogeologic analysis of regional systems
• Integrated surface-water/ground-water interpretations
• Conflict resolution, technical mediation of water issues
• USGS offices: Alaska (1978-79), Menlo Park (1979-84), San Diego (1985-present).
• Project Chief: all projects, listed below, involve optimal water-management, regional systems, surface-water/ground-water interaction, and conflict resolution.
• Advising: Optimal management of regional ground-water systems: Texas, New Mexico, Nebraska, Hashemite Kingdom of Jordan
• Teaching: Optimal ground-water management training courses (1994, 1997, 2005-07)
  

Research Interests:

• Real-world application of constrained optimization techniques
• Real-time water management
• Conflict resolution of water issues
• Integrated management of biologic/hydrologic resources
• Land deformation caused by ground-water recharge/extraction
  

Projects:

• San Bernardino Optimal Basin Management - http://ca.water.usgs.gov/sanbern
• San Diego Hydrogeology - http://ca.water.usgs.gov/sandiego
• Owens Valley - http://ca.water.usgs.gov/owens
• Temecula - http://ca.water.usgs.gov/temecula
• Enhancing Ground-water Management in Jordan - http://international.usgs.gov/projects/jd-groundwater.htm