TOPIC 2:

How does the challenge of predicting hazards differ between earthquakes

- at plate boundaries

- In plate boundary zones

- within plates?

Earthquake locations map narrow plate boundaries, broad plate boundary zones &

regions of intraplate deformation

INTRAPLATE

NARROW BOUNDARIES

DIFFUSE BOUNDARY ZONES

Stein & Wysession, 2003 5.1-4

PLATE BOUNDARY

PLATE BOUNDARY ZONE

INTRAPLATE

A. Newman

COLLISION BETWEEN INDIAN AND EURASIAN PLATES: SPACE GEODETIC MOTIONS.Mountain building by

continental collision produced boundary zone extending 1000’s of km northward from the nominal plate boundary at the Himalayanfront.

Total plate convergence taken up several ways. About half occurs across locked Himalayan frontal faults such as the Main Central Thrust

These faults are part of the interface associated with the underthrusting Indian continental crust, which thickens crust under high Himalayas.

Larson et al., 1999

COLLISION BETWEEN INDIAN AND EURASIAN PLATES: SPACE GEODETIC MOTIONS.

GPS data also show along-strike motion behind the convergent zone, in the Tibetan Plateau, presumably because the uplifted and thickened crust spreads under its own weight.

Extension is part ofa large-scale process of crustal "escape" or"extrusion" in which large fragments of continental crust are displaced eastward by the collision along major strike-slipfaults.

Larson et al., 1999

1900-2002

PACIFIC

NORTH AMERICA

PLATE BOUNDARY: SAN ANDREAS

30-45 mm/yr

PLATE BOUNDARY ZONE: 1-10 mm/yr OFF MAIN BOUNDARY

INTRAPLATE :

(< 1 mm/yr)

NORTH AMERICA - PACIFIC PLATE MOTION

48 mm/yr

CONTINENTAL STRIKE SLIP BOUNDARY ZONE

Stein, 1993

PLATE BOUNDARY

Most of the plate motion occurs on narrow (< 100 km wide) boundary

Earthquakes result primarily from plate motion

Earthquake recurrence directly reflects known plate motion

Earthquake locations don’t change for long time (Myr)

Past plate motion, present plate motion, geological, seismological, and geodetic rates

are consistent and so give consistent estimates of earthquake hazard

1906 SAN FRANCISCO EARTHQUAKE

USGS

Average 4 m of motion

West side moved north

Motion along hundreds of miles of San

Andreas Fault

Over many years, rocks on opposite sides of the fault move, but friction on the fault "locks" it

and prevents slip

Eventually strain stored is more than fault rocks can withstand,

and the fault slips in earthquake

Before plate tectonics, no idea why motion occurred

ELASTIC REBOUND MODEL PROPOSED

Even so, F. Omori used Japanese experience to predict that a similar earthquake was at least 100

years away

GPS FAR FIELD SLIP RATE 35 mm/yr

Z.-K. Shen

GEOLOGIC SLIP RATE - 3700 yr ~ 35 mm/yr

SAN ANDREAS FAULT

Locked strain will be released in next earthquake

Since last earthquake in 1857 ~ 5 m slip accumulated

mean 132 yr 105 yr

Sieh et al., 1989

Although time between earthquakes is variable

36 mm/yr * 132 yr ~ 5 m slip

~ magnitude 7.7 earthquake

Agreement between paleoseismology, plate motion, & GPS shows that large earthquakes

take up most of the motion

VARIATIONS IN RECURRENCE TIME MAY BE DUE TO DIFFERENCES IN EARTHQUAKE SIZE AND

STRESS TRANSFER

R. Stein et al., 1997

1900-2002

PACIFIC

NORTH AMERICA

PLATE BOUNDARY ZONE:

1-10 mm/yr OFF MAIN BOUNDARY

NORTH AMERICA - PACIFIC PLATE MOTION

48 mm/yr

PLATE BOUNDARY ZONE (1-10 mm/yr)

Some of the plate motion occurs in broad (< 1000 km wide) zone away from boundary

Earthquakes result from plate motion and local effects (topography)

Earthquake recurrence does not reflect known plate motion

Earthquake locations change on intermediate time (10 - 100 Kyr)

Geological, seismological, and geodetic rates are usually consistent and so give consistent

estimates of earthquake hazard

GPS site velocitiesrelative to

North America

San Andreas Fault system

Intermountain seismic belt

Eastern California shear zone

Colorado Plateau

PACIFIC - NORTH

AMERICA PLATE

BOUNDARY ZONE

Earthquakes away from

San Andreas

Bennett et al., 1999

Wasatch fault, Salt Lake City, Utah

M ~ 7 earthquakes in past 6000 years

None in past 500 years

GPS shows strain building up for future earthquakes

M 7 expected ~ 1000 yr from seismicity

GPS consistent - shows ~1-2 mm/yr extension

Chang et al., 2006

Stein et al., 2005

WASATCH FAULT: GPS & EARTHQUAKES AGREE 1 mm/yr -> 1 m/ 1000 yrs -> M7

PLATE INTERIOR (2< mm/yr)

Plate interior deforms slowly far away from boundary

Don’t know what causes earthquakes, probably indirect result from plate motion, mantle flow, and

local effects (topography, sediment, glacial)

Earthquake recurrence does not reflect known plate motion

Earthquake locations change on short time scales (100s - Kyr)

Geological, seismological, and geodetic rates can differ and so give different estimates of

earthquake hazard

CONTINENTAL INTRAPLATE EARTHQUAKES

Complex regional system of interacting faults

Seismicity migrates between faults due to stress transfer

Seismicity varies in space and time

Earthquakes can occur on fault for a while, then move

Past can be poor predictor

McKenna, Stein & Stein, 2007

A complex system - whose behavior depends on the

interactions between components that can’t be viewed in isolation

“Large continental interior earthquakes reactivate ancient

faults … geological studies indicate that

earthquakes on these faults tend to

be temporally clustered and that

recurrence intervals are on the order of

tens of thousands of years or more.”

(Crone et al., 2003)

Meers fault, OklahomaActive 1000 years ago, dead now

CONTINENTAL INTRAPLATE EARTHQUAKES ARE OFTEN EPISODIC, CLUSTERED & MIGRATING

during the periodprior to the periodinstrumental events

Earthquakes in North ChinaEarthquakes in North China

Large events often pop up where there was little seismicity!

OrdosPlateau

Sha

nxi G

rabe

n

Bohai Bay

Beijing

1303 HongtongM 8.0

Liu, Stein & Wang 2011

Weihi rift

during the periodprior to the periodinstrumental events

Earthquakes in North ChinaEarthquakes in North China

Large events often pop up where there was little seismicity!

OrdosPlateau

Sha

nxi G

rabe

n

Bohai Bay

Beijing

1556 HuaxianM 8.3

Weihi rift

Liu, Stein & Wang 2011

during the periodprior to the periodinstrumental events

Earthquakes in North ChinaEarthquakes in North China

Large events often pop up where there was little seismicity!

OrdosPlateau

Sha

nxi G

rabe

n

Bohai Bay

Beijing

1668 TanchengM 8.5

Weihi rift

Liu, Stein & Wang 2011

during the periodprior to the periodinstrumental events

Earthquakes in North ChinaEarthquakes in North China

Large events often pop up where there was little seismicity!

OrdosPlateau

Sha

nxi G

rabe

n

Bohai Bay

Beijing

1679 SanheM 8.0

Weihi rift

Liu, Stein & Wang 2011

during the periodprior to the periodinstrumental events

Earthquakes in North ChinaEarthquakes in North China

Large events often pop up where there was little seismicity!

OrdosPlateau

Sha

nxi G

rabe

n

Bohai Bay

Beijing

1966 XingtaiM 7.2

1976 TangshanM 7.8

1975 HaichengM 7.3

Weihi rift

Liu, Stein & Wang 2011

No large (M>7) events ruptured the same fault segment twice in past 2000 years

In past 200 years, quakes migrated from Shanxi Graben to N. China Plain

Historical

Instrumental

Shan

xi G

rabe

n

Weihi rift

Maps are like ‘Whack-a-mole’ - you wait for the mole to come up where it went down, but it’s likely to pop up somewhere else.

NEW MADRID SEISMICITY: 1811-12 AFTERSHOCKS?

Ongoing seismicity looks like aftershocks of 1811-12, as suggested by the fact that the rate & size are decreasing. Moreover, the largest are at the ends of the presumed 1811-12 ruptures

Stein & Newman, 2004

Rate-state friction predicts aftershock duration 1/loading rate

Plate boundary faults quickly

reloaded by steady plate motion after large earthquake

Faults in continents reloaded much more slowly, so

aftershocks continue much

longer

Stein & Liu, 2009

Long aftershock sequences in slowly deforming continental interiors

Stein & Liu 2009

Lots of seismicity may be aftershocks

Aftershock sequence of the 1976 Tangshan earthquake continues today (M. Liu)

Effect of major (5 MPa) weak zones

Complex space-time variability due to fault interactions via stress transfer

Seismicity extends beyond weak zones

Short-term seismicity does not fully reflect long-term

Variability results from steady platewide loading without local or time-variable loading

Hazard assessment based only on the recent earthquake record overestimates the risks in

regions of recent large earthquakes and underestimates them where seismicity has

been recently quiescent.

We are just beginning to study how mid-continent earthquakes work, but it seems that

often

1900-2002

PACIFIC

NORTH AMERICA

PLATE BOUNDARY:

Hazard assessment is reasonably good (“B”)

PLATE BOUNDARY ZONE:

Hazard assessment is adequate (“C”)

INTRAPLATE:

Hazard assessment is probably poor

(“D”)

All should be better in China due to longer earthquake record