2464-4

Earthquake Tectonics and Hazards on the Continents

S. G. Wesnousky

17 - 28 June 2013

Univ. of Nevada USA

Recognizing and characterizing strike-slip faults and earthquakes in USA

Strike-slip FaultsGeomorphic Expression, Slip Rate, and Repeat TimeTrieste 2013 Wesnousky

PhysiograhyGeomorphologyandFaulting

A Strike-Slip Fault

Fault

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An earthquake is the result of a sudden displacement across a fault that releases stresses that have accumulated in the crust of the earth.

Mckay’s 1890 report on the 1888 Hope Fault Earthquake, NewZealand

Koto’s 1893 report on the 1891 Neodani Earthquake, Japan

Gilbert’s 1884 paper on theorey of earthquakes in the Great Basin and 1910 account of the 1906 San Francisco earthquake, United States.

1992 d

1999 Hector Mine

1992 Landers

The repetition of this process results in distinct geomorphic features along fault zones that may be

interpreted by geologistsTo determine the rate, style, and magnitude of fault slip

Calculation of slip rateand earthquake repeat time

San Andreas “Rift”

Pt. Arena

Pt. Reyes

Strike-slip displacement

• juxtaposition of topography

• cataclasis and weakening of rock in fault zone

• stream capture along fault

• preferential erosion along fault

leads to long linear ridges and valleys...

Gualala River

ViewNorth

toCoast

Tomales and Bolinas Bays north of San Francisco Bay

San Andreas Lake

Monterey

Central San Andreas

Carrizo Plain

example of offset stream

San Andreas

linearity of tracealternate-facing scarps

San Andreas isCarrizo Plain

Sag Ponds

linearity of tracealternate-facing scarpssag ponds

Cataclasis in fault zone leads to increase in volume of sediments - Small component of contraction in additon to strike-slip

can lead to uplift and folding alongfault zone - sometimes referred to as ‘flower structure’

linear tracein Carrizo Plain

Incision on hanging/uplifted wall.... offset and abandoned streams

Channel abandoned 3700 ybp 128 meters

San Andreas slip rate = 128m / 3700 years = ~ 34 mm/yr Sieh and Jahns (1984), GSAB v. 95,

883-896

Calculation of fault slip rate...

Offsets D = 9 to 12 minterpreted to be result ofsingle earthquake...

Average Repeat Time = 9 to 12 m / ~34 mm/yr = 250 to 450 years Sieh and Jahns (1984), GSAB v. 95,

883-896

Calculation of Repeat Time...

Slip Rate =

~210m / ~17kyr = ~ 12 mm/yrRockwell et al (1990), JGR, v. 95, 8593-8605

Offset and beheaded stream

Strike Slip Faults are often long and quite linear - but they are not always continuous

Step:~3km Step:~3km

Step:~3kmLake Elsinore 0 50km

4: WHITTIER-ELSINORE FAULT ZONE: SS 10-15KM; LENGTH ~ 240KMCorona

Coyote

Mtns.Agua Tibia Mtn.

WHITTIER

N

LAGUNASALADA

Baldwin

Hills Rosecran

Hills Dominguez

HillsSignal

Hill

Step: ~ 3km Steps:~ 2km

Pacific Ocean

NewportBeach

3: NEWPORT- INGLEWOOD FAULT: SS~0.2-10KM; LENGTH = 60KM

0 20kmStep: ~ 2km

Long

Beach

NSA

NT

A M

ON

ICA

FAU

LT

2: GARLOCK FAULT; SS~ 64KM; Length ~ 240KM

Step~3km

Step ~1/2km0 50kmFremont Valley

Koehn Lake

NSearles

Valley

Garlock Fault D=64 km

5: SAN JACINTO FAULT: SS 25 KM; LENGTH ~ 230KM

Step ~4km Step ~ 4km Steps ~ 5km & 1 km

Step: ~ 5km50

Hemet

SUPERSTITIONBORREGO

COYOTE

CLARE-MONTANDREAS

Loma

Linda

CLARKE

CASA LOMA

0 kmN

SAN

Pearblossom to Bombay Beach

0 50kmCholame to Little Rock Reservoir

Cholame

PearblossomN

Los Gatos to CholameSan Juan Bautista

Los Gatos

N

Step~1km Cholame

Parkfield

1&12: SAN ANDREAS FAULT: SS ≥150 KM; LENGTH ~ 1000 KM

N

Pt. Arena Pacific Ocean Golde

nGate

Pt. Arena to BelmontLosGatos

N

Bitterwater

Little Rock

Yucaipa BomBay Beach

Little RockReservoir

IndioWrightwood Cajon Pass

San Andreas D=150 km

San Jacinto D=25 km

Whittier-Elsinore D~15 km

Newport-Inglewood D=10 km

Structural Evolution of Faults

and Fault Systems?

Seismological Evolution of Faults

and Fault Systems?

Strike-Slip Faults of California

Long, linear, but NOT continuous

D is estimate of total strike-slipsince birth of fault

Structural Evolution of Faults - tend to simplify with accumulated offset

(0-1

steps

/75km

)

Co

mp

lexi

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step

s/km

)

0.001

0.01

0.1

0.1 1 10 100 1000

(0-1

steps

/75km

)

S. and Baja CalifCo

mp

lexi

ty (

step

s/km

)

Cumulative Strike-Slip (km)

N. Calif.

Japan

New Zealand

China

Turkey

How do discontinuities (steps) in fault trace effect the propagation of earthquake ruptures?

contraction

extension

Compilation of 20+ strike-slip surface-rupture earthquakes..

can be importantto hazardanalysis...

Is termination of STRIKE-SLIP rupture associated with step in fault trace of dimension >=1km or end of active fault trace ?

Summary of behavior of all discontinuities along strike of historical earthquake ruptures.