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,

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 Himalayan front. 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 of a large-scale process of crustal "escape" or "extrusion" in which large fragments of continental crust are displaced eastward by the collision along major strike-slip faults. Larson et al., 1999

PACIFIC NORTH AMERICA PLATE BOUNDARY: SAN ANDREAS 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 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

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 ( Kyr) Geological, seismological, and geodetic rates are usually consistent and so give consistent estimates of earthquake hazard

GPS site velocities relative 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, Oklahoma Active 1000 years ago, dead now CONTINENTAL INTRAPLATE EARTHQUAKES ARE OFTEN EPISODIC, CLUSTERED & MIGRATING

during the period prior to the period instrumental events Earthquakes in North China Large events often pop up where there was little seismicity! Ordos Plateau Shanxi Graben Bohai Bay Beijing 1303 Hongtong M 8.0 Liu, Stein & Wang 2011 Weihi rift

during the period prior to the period instrumental events Earthquakes in North China Large events often pop up where there was little seismicity! Ordos Plateau Shanxi Graben Bohai Bay Beijing 1556 Huaxian M 8.3 Weihi rift Liu, Stein & Wang 2011

during the period prior to the period instrumental events Earthquakes in North China Large events often pop up where there was little seismicity! Ordos Plateau Shanxi Graben Bohai Bay Beijing 1668 Tancheng M 8.5 Weihi rift Liu, Stein & Wang 2011

during the period prior to the period instrumental events Earthquakes in North China Large events often pop up where there was little seismicity! Ordos Plateau Shanxi Graben Bohai Bay Beijing 1679 Sanhe M 8.0 Weihi rift Liu, Stein & Wang 2011

during the period prior to the period instrumental events Earthquakes in North China Large events often pop up where there was little seismicity! Ordos Plateau Shanxi Graben Bohai Bay Beijing 1966 Xingtai M Tangshan M Haicheng M 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 Shanxi Graben 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: AFTERSHOCKS? Ongoing seismicity looks like aftershocks of , as suggested by the fact that the rate & size are decreasing. Moreover, the largest are at the ends of the presumed 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

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