Slip rate uncertainty: Examples from the Calico and Lenwood faults

Dr. Mike OskinDepartment of Geological SciencesUniversity of North Carolina at Chapel Hill

Co-PI: Lesley Perg

Students: Mike Strane, Emily Gurney, Eitan Shelef, Dylan Blummentritt

Collaborators: Alex Iriondo, Brad Singer, Sujoy Mukhopadhyay

Lesley

Eitan

Emily Mike

Geodesy12 ± 2 mm/yr

Paleoseismology5 to 7 mm/yr (Estimate)

Central Mojave Transect

Paleoseismic clusters from the ECSZ south of Barstow

From T. Rockwell, S. Lindvall, and C. Rubin

Well-constrained

Poorly-constrained

Earthquake Timing

Recent cluster began ~1000 ka

Average Earthquake Recurrence of 3 to 9 kyr

Alluvial Fan Markers of Fault Slip

Active Wash Surface

Alluvial Fill

Abandoned Wash Surface

Development of Alluvial Fan Stratigraphy

Desert Pavement

Soil Development

Central Mojave Transect

Lenwood

Calico

Helendale

Camp Rock

Pisgah-Bullion

Ludlow

Pipkin Cinder Cone 740±40 ka

Sheep Spring Wash

3 kmCalico Fault

Slip Rate Measurement

s

SRTM Topography

Area of LIDAR

CalicoFault

Oskin et al. (2007)

Q2a

K

F

Q2b

Q1 B

QTcg

SlipRates

Plio-Quaternary Growth Strata

Fanning Dips

Q1 Fan: First occurrence of ca. 740 ka basalt clasts in growth section

Tilted Q1 Alluvial Fan

661 ± 20 ka 3He Exposure Date on one basalt clast

Restorationof Q1 Fan

Displacement

900 ± 200 meters

Age: 650 ± 100 ka

1.4 ± 0.4 mm/yr

Today

~300 ka?

650 ka

Cosmogenic Exposure Dating

qtz

ol

nn

X

+

10Be: t1/2 = 1.5 Myr

3He: stable, rare

Q2b Fan Surface

Quartz and Basalt PebbleDesert Pavement

Quartz Monzonite & Basalt Boulders

Cosmogenic Dates from Q2b Terrace and Modern Wash

0

50

100

150

200

250

300

Age

(ka

) Quartz Monzonite 10Be Basalt 3He

Boulders

Pavement

Wash Boulders

BouldersPavement

Wash Boulders

10Be Age - Inheritance: 56.4 ± 7.7 ka (2)

Lithology-Dependent Hillslope Residence Time

Restoration of Q2a Terrace Displacement

100 ± 10 meters 1.8 ± 0.3 mm/yr(95% confidence, Errors summed as root mean square)

Central Mojave Transect

Lenwood

Calico

Helendale

Camp Rock

Pisgah-Bullion

Ludlow

Lenwood FaultSlope Map: Darker = SteeperQ2b

Slip Rate: 0.8 +0.2/-0.3 mm/yr

Central Mojave Transect

Lenwood Fault

Calico Fault

Helendale Fault

Camp Rock Fault

Pisgah-Bullion Fault

Ludlow Fault

0.8 ± 0.2 mm/yr 1.8 ± 0.3 mm/yr

≤0.8 ± 0.2 mm/yr ≤1.4 ± 0.6 mm/yr ≤0.4 ± 0.2 mm/yr

Total: ≤6.1 ± 1.9 mm/yr

1.0 ± 0.2 mm/yr

(95% confidence, errors summed as root mean square,10Be production rate uncertainty added after summation)