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
Site Location- northern San Jacinto fault zone
• topography along the fault zone (google earth?)
Image from
2
Mystic Lake Site
Mystic Lake site seen in 1940 Air
Photo
NE
southeast wall
SW
3 more shallow trenches in
2010- saw same relationships.
Trench 6
Trench 7
Depositional
model
1. Event on SW fault strand causes subsidence
2. Sag fills with clay, silt, sand
3. Soil layer develops
4. Repeat
NE
southeast wall
SW
17381853
1670-1828
1521-1616
1349- 1445
10761258
807- 961
579- 845
Years AD
Mystic Lake events
1670-1828
Recurrence Interval=
159 to 210 years
normalized probability density functions
1829
1574
1428
1189
888
711
1
.5
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