Earthquake recurrence models

Are earthquakes random in space and time?We know where the faults are based on the geology and geomorphology•Segmentation•Classical models•Next generation models and tests

Burbank and Anderson

Basic fault segmentation

Fault zone is comprised of heterogeneous non coplanar fault surfaces bounding oblate blocks whose geometry and activity varies in time and space

Map view mode II step

(bend)

Cross-section view

mode III step (bend)

3D mixed mode

stepover

Strong influences on •Stress and displacement fields around the fault surfaces•Further development and linkage•Fluid flow•Rupture dynamics•Fault zone strength

Questions:Geometric—Fault surface and block shapes and sizesTime—How long are they active? What is slip history? Block motion history?Development—Linkage and evolution of roughness

Burbank and Anderson

Predicting the endpoints of earthquake ruptures (I)

Wesnousky, 2006

Predicting the endpoints of earthquake ruptures (II)

Wesnousky, 2006

“stop light color scheme”

About 2/3 rupture terminations are associated with discontinuities or fault ends

Ste

p si

ze

A. Periodic earthquake model in which stress levels at the time of rupture and after it are known. These yield a predictable time and slip for each earthquake. B. Time-predictable model based on a consistent stress level at which failure occurs. Stress drop and slip magnitude are unpredictable, but given previous slip, time until the next earthquake (with unknown slip) is predictable. C. Slip-predictable model based on a consistent stress level at the end of an earthquake. Given time since the last rupture, magnitude of slip is predictable. Modified after Shimaki and Nakata (1980) Burbank and Anderson

1984

“…individual faults and fault segments tend to generate essentially the same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum.”

Burbank and Anderson

If we know slip rate du/dt

And we assume u(x) per event

We can get recurrence time

uave or umax per event should also imply length and M

Zielke and Arrowsmith, in prep.

Modeling earthquake recurrence

Past and Future Earthquakeson the San Andreas Fault (I)

Weldon, et al., 2004

Weldon, et al., 2005

Weldon, et al., 2005

Cartoon of paleoearthquake extent based on (up-to) 2005 event timing (vertical bars)

Northern 2/3 and southern 1/3 repeating events

Random in time and length

Long with a few small events

Three recent developments strengthen the hypothesis that the fault breaks in relatively infrequent, large earthquakes:

1) Relatively large slip/event has been documented implying long rupture length (4-7 m = >100km)

2) Dating uncertainty and 3) Event quality uncertainty

Current 151 year hiatus not unusual. When it ends, a substantial portion of the fault is likely to rupture either as a single long rupture or a series of overlapping ruptures in a short time interval