In the past ~15 years we’ve learned a lot and have new questions: Paleoseismology shows that continental intraplate seismicity often migrates, is episodic, and clustered. How? Why? GPS shows that deformation in continental interiors is much slower than we expected (< 2 mm/yr). Why don’t we see the coherent deformation fields expected from plate driving force models? How do earthquakes relate to the deformation? Short earthquake records don’t capture long term hazard. How can we use new results for improved hazard estimation? Continental Intraplate Deformation & Seismicity: What We Know, What We Don't, and What We Need To

“Large SCR earthquakes reactivate ancient faults. Earthquakes on these faults tend to be temporally clustered and have recurrence intervals on the order of tens of thousands of years or more.” (Crone et al., 2003) “During the past 700 years, destructive earthquakes generally occurred in different locations, indicating a migration of seismicity with time.” (Camelbeeck et al., 2007) Why? Stress transfer, stress variations, fault healing vs loading rate, fluids… NW Europe Australia & US

STUDY MOTIONS WITHIN PLATES WITH GPS Site motions show that eastern North America behaves like a very rigid plate The difference between the observed motion and that predicted for an ideal rigid plate is less than 2 mm/yr Stein & Sella 2002 Stein & Wysession, 2003 RIGID INTERIOR DEFORMING PBZ

The most visible motion in Eastern North America is post-glacial rebound Sella et al., 2007

Horizontal GPS data don’t show the coherent intraplate motion expected from the World Stress Map and driving force models Sella et al., 2007 Richardson & Reding, 1991 WSM 2005

Wasatch: NA/PA PBZ M 7 expected ~ 1000 yr from seismicity GPS consistent - shows ~1-2 mm/yr extension Chang et al., 2006 Stein et al., 2005 COHERENT 1 mm/yr SHOULD BE VISIBLE

Hungary Pannonian Basin Intracontinental Eurasia Diffuse seismicity, migrates M max observed = 6.2 M 7 expected ~ 1000 yr from seismicity GPS consistent - shows ~1-2 mm/yr shortening (Grenerczy et al., 2000) Toth et al, 2004

SHORT RECORD OF SEISMICITY & HAZARD ESTIMATE Predicted hazard from historic seismicity is highly variable Likely overestimated near recent earthquakes, underestimated elsewhere More uniform hazard seems more plausible - or opposite if time dependence considered Map changes after major earthquakes Africa-Eurasia convergence rate varies smoothly GSHAP NUVEL-1 Argus et al., 1989

SHORT RECORD OF SEISMICITY & HAZARD ESTIMATE Predicted hazard from historic seismicity is highly variable Likely overestimated near recent earthquakes, underestimated elsewhere More uniform hazard seems more plausible - or opposite if time dependence considered Map changes after major earthquakes Africa-Eurasia convergence rate varies smoothly GSHAP NUVEL-1 Argus et al.,

M>7 Long record needed to see real hazard Swafford & Stein,

Peak Ground Acceleration 10% probability of exceedance in 50 years (once in 500 yr) GSHAP (1999) Present Study HUNGARY: ALTERNATIVE HAZARD MAPS Concentrated hazard inferred from historic seismicity alone Diffuse hazard inferred incorporating geology Toth et al., 2004

Basel 1356 M~ Lots to do! Newcastle, Australia 1989 M 5.6

Most earthquakes occur on either narrow plate boundaries or broad plate boundary zones INTRAPLATE NARROW BOUNDARIES DIFFUSE BOUNDARY ZONES The comparatively rare, hence hard to study, ones in the interior of plates have scientific & societal interest

HUNGARY - PANNONIAN BASIN (INTRACONTINENTAL EURASIA) Diffuse seismicity, migrates M max observed = 6.2 M 7 expected ~ 1000 yr from seismicity GPS consistent - shows ~1-2 mm/yr shortening (Grenerczy et al., 2000) Toth et al, 2004 Grenerczy & Kenyeres,

In the past ~15 years we’ve learned a lot: - Paleoseismology shows that continental intraplate seismicity often migrates, is episodic, and clustered - GPS lets us distinguish a broad plate boundary zone from a plate interior GPS shows that deformation in continental interiors is much slower than we expected (< 2 mm/yr) - We don’t see the coherent deformation fields we expected from plate driving force models - We need to understand the mechanics - Even so, these new results are leading to improved hazard models

Basel 1356 M~ Continental Intraplate Deformation & Seismicity: What We Know, What We Don't, and What We Need To Newcastle, Australia 1989 M 5.6

?? 9k7k6k4k12k3k1kToday Portageville CycleReelfoot CycleNew Madrid Cycle Slip Cluster Slip Cluster Slip Cluster Quiescent Holocene Punctuated Slip New Madrid earthquake history inferred from Mississippi river channels Holbrook et al., 2006 “During the past 700 years, destructive earthquakes generally occurred in different locations, indicating a migration of seismicity with time.” (Camelbeeck et al., 2007)

Sella et al., 2007 Canada rises & US sinks Hinge line agrees with lake level data The most visible GPS motion in Eastern North America is post-glacial rebound