New paleoseismic data from the northern San Jacinto Fault Zone, southern California

New paleoseismic data from the northern San Jacinto Fault Zone, southern California

Nate Onderdonk (CSULB)Tom Rockwell (SDSU)Sally McGill (CSUSB)

Gayatri Marliyani (SDSU)

Funded by SCEC

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• topography along the fault zone (google earth?)

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Image from http://www.atmos.ucla.edu/~alexhall/res.html

Site Location- northern San Jacinto fault zone

San Andreas Fault

San Jacinto Fault

Mystic Lake Site

Mystic Lake site seen in 1940 Air Photo

NE SWsoutheast wall

3 more shallow trenches in 2010- saw same relationships.

Trench 6

Trench 7

Depositional model1. Event on SW fault strand causes

subsidence2. Sag fills with clay, silt, sand3. Soil layer develops4. Repeat

NE SWsoutheast wall

1738- 1853

1521-1616

1349- 14451076- 1258

807- 961

579- 845

Years AD

1670-1828

Mystic Lake events normalized probability density functions

1 .5

1829

15741428

1189

888

711

1670-1828

Recurrence Interval= 159 to

210 years

Comparing Mystic Lake events to Hog Lake record

?

?

Comparison with SAF record

Comparison with Wrightwood record

Conclusions

Mystic Lake is a great source of paleoseismic info for the SJF and has potential for a long record

Shallow trenches show evidence for 7 events in past 1700 years (avg. RI = 185 years)

Non-Conclusions

Some events may correlate with Hog Lake events? and maybe Wrightwood as well?

if so: San Jacinto step-over is not a segment boundary, and neither is juncture with SAF

400m long trench

Correlated stratigraphy across the entire sag

SW fault zone is locus of activity