In the past ~15 years we’ve learned a lot and have new questions: Paleoseismology shows that...
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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
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Transcript of In the past ~15 years we’ve learned a lot and have new questions: Paleoseismology shows that...
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 GPSSite motions show that eastern North America behaves
like a very rigid plateThe difference between the observed motion and that predicted for an ideal rigid plate is less than 2 mm/yr
Stein & Sella2002
Stein & Wysession, 2003
RIGID INTERIOR
DEFORMING PBZ
The most visible motion in Eastern North America ispost-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
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
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-1Argus 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-1Argus et al., 1989
2004
2003
M>7
Long record needed to see real hazard
Swafford & Stein, 2007
1963-2004
Peak Ground Acceleration10% probability of exceedance
in 50 years(once in 500 yr)
GSHAP (1999)GSHAP (1999)
Present StudyPresent Study HUNGARY: ALTERNATIVE HAZARD MAPS
Concentrated hazard inferred from historic seismicity alone
Diffuse hazard inferred incorporating geology
Toth et al., 2004
Basel 1356 M~6.0-6.5
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
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
Grenerczy & Kenyeres, 2004
1995-1999
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~6.0-6.5
Continental Intraplate
Deformation & Seismicity:
What We Know, What We Don't, and What We Need
To
Newcastle, Australia 1989 M 5.6
? ?
9k 7k 6k 4k12k 3k 1k Today
Portageville Cycle Reelfoot Cycle New Madrid Cycle
Slip
Cluster
Slip
Cluster
Slip
ClusterQuiescent Quiescent 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
