Continental Intraplate Deformation & Seismicity:

1. Continental Intraplate Deformation & Seismicity: What We Know, What We Don't, and What We Need To In the past ~15 years we’ve learned a lot andhave 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?

2. Australia & US “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) NW Europe Why? Stress transfer, stress variations, fault healing vs loading rate, fluids…

3. 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 & Sella2002 RIGID INTERIOR DEFORMING PBZ Stein & Wysession, 2003

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

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

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

7. Hungary Pannonian Basin Intracontinental Eurasia Diffuse seismicity, migrates Mmax 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

8. SHORT RECORD OF SEISMICITY & HAZARD ESTIMATE Africa-Eurasia convergence rate varies smoothly NUVEL-1 Argus et al., 1989 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 GSHAP

9. SHORT RECORD OF SEISMICITY & HAZARD ESTIMATE Africa-Eurasia convergence rate varies smoothly NUVEL-1 Argus et al., 1989 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 2003 2004 GSHAP

10. 1963-2004 Long record needed to see real hazard M>7 Swafford & Stein, 2007

11. HUNGARY: ALTERNATIVE HAZARD MAPS Present Study Peak Ground Acceleration10% probability of exceedance in 50 years(once in 500 yr) Diffuse hazard inferred incorporating geology GSHAP (1999) Concentrated hazard inferred from historic seismicity alone Toth et al., 2004

12. Newcastle, Australia 1989 M 5.6 Lots to do! Basel 1356 M~6.0-6.5

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

15. HUNGARY - PANNONIAN BASIN (INTRACONTINENTAL EURASIA) Toth et al, 2004 1995-1999 Grenerczy & Kenyeres, 2004 Diffuse seismicity, migrates Mmax observed = 6.2 M 7 expected ~ 1000 yr from seismicity GPS consistent - shows ~1-2 mm/yr shortening (Grenerczy et al., 2000)

16. 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 interiorGPS 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

17. Newcastle, Australia 1989 M 5.6 Continental Intraplate Deformation & Seismicity: What We Know, What We Don't, and What We Need To Basel 1356 M~6.0-6.5

18. Holocene Punctuated Slip 12k 9k 7k 6k 4k 3k 1k Today ? Slip Cluster Slip Cluster Slip Cluster ? Quiescent Quiescent Quiescent Portageville Cycle Reelfoot Cycle New Madrid Cycle “During the past 700 years, destructive earthquakes generally occurred in different locations, indicating a migration of seismicity with time.” (Camelbeeck et al., 2007) New Madrid earthquake history inferred from Mississippi river channels Holbrook et al., 2006

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