Transcript San Jacinto fault: Mystic Lake

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