SCEC Award Number 15149 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Paleoseismology of the tsunamogenic Long Point fault, Santa Catalina Island
Investigator(s)
Name Organization
Simon Klemperer Stanford University
Other Participants Mark Legg (Legg Geophysical Inc.),
Danny Brothers (Pacific Coastal & Marine Science, USGS Santa Cruz) Chris Castillo, Stanford University Undergraduate TBD for geochronology lab. work, Stanford University
SCEC Priorities 1a, 1d, 4a SCEC Groups Geology, Seismology, Geology
Report Due Date 03/15/2016 Date Report Submitted 03/13/2016
Project Abstract
 The newly mapped Long Point Fault on and offshore Catalina Island presents a significant tsunamogenic hazard to nearshore communities in the Los Angeles area. We have constrained slip rate and recurrence interval for the Long Point Fault by dating marine terrace deposits transected by the fault. Strata overly-ing landslide deposits likely triggered by the Long Point fault have been dated using the overlying and underlying sequence boundaries. Even modest tsunamogenic landslides (whether or not seismically triggered) can be very dangerous because of the lack of warning to coastal communities. In June 2015 we conducted 2 days of chirp profiling to locate sequence boundaries within reach of our coring machine, and 2 days of coring and Van Veen grab sampling. The success of these dives motivated two E/V Nautilus ROV dives to collect additional samples that will further refine our chronology. 10 samples have been dated using 14C and U-series geochronology, and we have measured δ18O and δ13C on about 50 samples. Samples yielding forams and molluscs have been analyzed and age ranges for several marine terraces have been confirmed, yielding a robust chronology for Catalina's terraces, and demonstrating our ability to use the same approach on other seamounts.
Intellectual Merit The SCEC vertical motion database lacks uplift rates for the numerous submerged seamounts and wave-planed features in the southern California Borderland, and is thus biased toward sampling uplift. Our method of using submerged terraces to investigate paleoseismology and vertical deformation addresses this deficiency and presents a clearer picture of vertical deformation in the SCCB. The submerged marine terrace method we have developed has potential applications in 12% of the borderland, and will elucidate uplift and subsidence records for numerous unexplored regions of the Southern California Borderland, enabling us to better understand evolving styles of deformation, as well as changes in the distribution of slip along the anastamosing faults that dissect the borderland.
Broader Impacts This SCEC funded project has received lots of publicity, including articles in the LA Times and Newsweek, invited talks at AGU and the Catalina Island Conservancy Symposium. E/V Nautilus Dives (36 hours total) were broadcast worldwide via telepresence to classrooms around the world, and were some of the most popular dives during the season. Our intern, Ethan Williams, participated in CHIRP and coring cruise and completed onshore processing of samples. He gained basic skills in seismic and CHIRP processing, and was trained to conduct U-series chronology in the Stanford ICPMS Facility.
Exemplary Figure FIGURE 3: Interpretation of seismic line Stanford 2610, SSW to NNE offshore Avalon, Santa Catalina Island. Bold lines indicate interpreted regressive/transgressive surfaces. Floor of submarine canyon adjacent to location of seismic profile shown as dashed line. Tortuous black line is bathymetric record of ROV dive track, close to the canyon floor but with excursions up the side walls. Red dots indicate locations of samples (both ROV and cores). Interpreted ages of major sequence boundaries labeled. Photos (left to right): a. wave rounded cobbles found in marine terrace deposits, evidence of fossil beaches. b: ROV grab sample of marine terrace, c: NA067-007, fossil bearing bryozoan marl recovered from ROV dive.
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