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