Is San Diego Ready For The 'Big One'?

SAN DIEGO -- Could an earthquake as large as the one the devastated China hit San Diego, and if it did, would the city be prepared?

Experts said without a doubt, San Diego could be hit with a powerful earthquake at any time. But the threat might not be as ominous as you think.

"If there's any good news about the China earthquake for us it's we cannot have an earthquake that big and devastating in San Diego," said Dr. Pat Abbott, professor of geology at SDSU.

Abbot said that's because the faults in San Diego are not capable of producing the same dramatic movement. Abbot said the biggest threat is the San Andreas Fault, about 80 miles away, which is overdue for a "big one." The fault is capable of 7.9.

"The high-frequency shaking tends to die down with distance -- but the kind that doesn't is the longer period," Abbott said.

Those low-frequency movements that could sway and potentially topple high-rises and bridges are the situations for which ta special team of first-responders in San Diego County is trained.

"Our teams are most focused on individuals that are truly trapped in heavy structures that have collapsed, or entombed is how we say it," said Jeff Frazier of the Urban Search and Rescue Task Force.

Frazier is a firefighter and leader with the search and rescue task force. He worked recovery after the Oklahoma City bombing and Sept. 11.

"We've done a lot to be prepared and to be able to respond," he said.

Abbott said the largest local threat is the Rose Canyon Fault, which runs under the city and north along the Interstate 5 corridor. That fault could produce up to a magnitude 7.0 quake.
He said older brick buildings would likely crumble, especially those not upgraded to earthquake standards.

Abbott said the death toll from a Rose Canyon quake could range from zero to 30 -- not even close to the devastation seen in China.

Source: NBCSandiego.com

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Thesis Defense - Spring 2008 - Sarah Johnson

Physical, petrological, and chemical trends associated with the conversion of k-feldspar-absent quartz dioritic and tonalitic conestones to saprolite in a meditteranean (hot summer) climate, Santa Margarita Ecological Reserve (SMER), southern California, U.S.A

Sarah Johnson
M.S. Candidate
Department of Geological Sciences
San Diego State University
Advisor Dr. Gary Girty

Friday, May 9th

ABSTRACT
W. Nesbitt and colleagues proposed that weathered plutonic material will spread linearly from parental fields subparallel to the A-CN join toward the A-K join on A-CN-K diagrams, and followed by a linear trend subparallel to the A-K join towards the A apex. Such linear trends are common because soil solutions are typically supersaturated with respect to K, but not CN. At SMER, our studies reveal a weathering trend that deviates from that proposed by W. Nesbitt and colleagues. SMER lies within a Mediterranean (hot summer) climate with an average precipitation of ~39.4 cm/yr and average temperature of ~16.6˚C. We sampled corestone and adjacent saprolite in an ~123 Ma tonalite, and at two sites lying within an ~107.5 Ma quartz diorite for thin section, physical properties, and chemical analyses. We used the chemical index of alteration (CIA) to determine the degree of weathering and used the transport function (τ) for assessing changes in elemental mass. Each variety of sampled corestone lacks modal K-feldspar but contains 4.50% to 12.0% biotite. Our thin section study of samples of saprolite suggests the following order, from most to least weathered; biotite, amphibole, plagioclase, and quartz. On A-CN-K diagrams saprolitic samples spread linearly from the parental material away from the K apex toward the A-CN join. XRD and microscope analyses indicate that this trend is due to the conversion of biotite to the mixed-layer expandable clays vermiculite-illite and vermiculite-smectite. The transport function, (τ), indicates that during this conversion K, Rb, and to a lesser extent Ba mass was consistently removed at the level of our sampling traverses by migrating paralithic fluids. In contrast, zero to only minor increases or decreases in the masses of most other elements reflect the spatially inconsistent and varied activity of eluviation and illuviation processes within the paralithic zone. Our data consistently suggest that in plutonic rocks lacking K-feldspar, biotite weathers more readily than plagioclase, and, as a result, it controls the direction of weathering trends in A-CN-K space. As noted above, the signature of this process is a trend in saprolitic samples extending from unweathered parental plutonic material away from the K apex and toward the A-CN join. Once biotite has been completely altered, then the weathering of plagioclase should produce a new trend extending subparallel to the A-CN join and toward the A apex. Under the Mediterranean (hot summer) conditions at SMER our data appear to have captured the first step in the initiation of this process.

Thesis Defense - Spring 2008 - Wallace Sconiers

The feasibility of antipodal volcanism as a result of the K/T impact

Wallace Sconiers
B.S. Candidate
Department of Geological Sciences
San Diego State University
Advisor Dr. Jared Morrow

Friday, May 9th

ABSTRACT
Research regarding the impact event at the Cretaceous-Tertiary (K/T) boundary at Chicxulub, Yucatan Peninsula, and the Deccan flood basalts of Western India has shown both possibility and dismissal of the two as being a series of interrelated events, although most workers agree that both sides were relatively antipodal at the K/T boundary. Subsequent 2D & 3D computer models following the development of Simplified Arbitrary Lagrangian-Eulerian (SALE) and similar code have shown that axial focusing of seismic waves following an impact for a planet analogous to earth is most significant at ~100 km depth below the antipode surface. However, calculations of the initial kinetic energy, total seismic energy produced as a function of the seismic efficiency for a C2 Chondrite bolide impact, and total energy delivered to a basaltic volume near its melting point at a depth of ~100 km generate a thermal pulse, or sudden change in temperature, of 1 millikelvin. This temperature increase is not sufficient to create or enhance pre-existing melts at depth.
Estimates of the total volume of lavas produced at the Deccan traps range from 1 x 10^5 to 1 x 10^6 km^3 over a duration of ~1 m.y., with average intervals between eruptions of sub-groups within the traps of 2-10,000 years. A stratigraphic section composed of main eruptive units within the traps shows one sub-group, the Wai, which is responsible for 50% of the total eruption volume from 66 to 64.5 Ma, peaking with the Ambenali Formation within the sub-group producing 200,000 km^3 of basalt 66 to 65.5 Ma. Activity substantially drops during the last two formations within the sub-group, Panhala and Desur, producing 25,000 and 10,000 km^3, respectively. A ~65 Ma date for the K/T impact would have had no effect on the Deccan trap system whose eruptive volumes were dropping per successive formation at this time.