Inferring Viscous Properties of the Lithosphere

Berkeley.edu ^ | Project Duration In Progress | Andy Freed and Roland Bürgmann

[BenLurkin]

a) Calculated coseismic Coulomb stress changes associated with the 1992 Mw=7.3 Landers (L), Mw=6.2 Big Bear (BB), and Mw=6.1 Joshua Tree (JT) earthquakes. Stresses are shown on the surface and through a cross-section that passes through the eventual rupture surface of the 1999 Mw=7.1 Hector Mine (HM) earthquake. Positive Coulomb stress changes indicate regions where neighboring faults (aligned parallel to the cross-section shown) have been pushed closer to failure. Note how a large reservoir of stress develops in the lower crust and upper mantle beneath the eventual Hector Mine hypocenter (star). Stresses in these regions cannot be sustained and begin to relax immediately after the Landers quake. (b) shows that after 7 years of relaxation (in this case the upper mantle is assumed to relax), much of the stress has transferred from the mantle to the upper crust leading to a build-up of Coulomb stress at the Hector Mine hypocenter. This transfer of stress is thought to have played an important role in explaining why the Hector Mine earthquake occurred only 7 years after the Landers quake despite both faults having repeat times in the 1000s of years.

http://seismo.berkeley.edu/~burgmann/RESEARCH/research_andy_2.jpg

[BenLurkin]

http://seismo.berkeley.edu/~burgmann/RESEARCH/research_andy_2.jpg

[BenLurkin]

Accelerated Stress Buildup on the Southern San Andreas Fault and Surrounding Regions Caused by Mojave Desert Earthquakes

Andrew M. Freed and Jian Lin (Woods Hole Oceanographic Institution)

Summary

“Scientists have hypothesized for decades that one major earthquake can trigger another earthquake on a nearby fault through stress interaction. More recent studies have further suggested that this interaction may be delayed by the slow viscous creeping of rocks in the Earth’s lower crust and upper mantle. This is best illustrated by the 1999 magnitude 7.1 Hector Mine earthquake, which occurred only 30 km away from the 1992 magnitude 7.3 Landers quake, but seven and half years later. The delay between these events can be explained by viscous flow consistent with observations of continuous ground deformation following the Landers quake (Freed and Lin, 2001).

In our more recent study (Freed and Lin, 2002), we further calculated how the Landers, Hector Mine, and two other earthquakes in the Mojave Desert have changed stresses on the nearby southern San Andreas and adjacent fault systems.”

http://seismo.berkeley.edu/seismo/annual_report/ar01_02/node25.html

[Smokin' Joe]

Interesting, thanks for posting this. While it seems intuitive that relief of stresses in one locale would transfer them to another, I had not considered that the transfer would happen that deep.

[BenLurkin]

There was a 3.1 earthquake on the Calico fault this morning. I thought I remembered hearing that the Hector Mine quake was on that fault(it was) — was researching it and came across these articles.

[SunkenCiv]

A name like Calico, I wouldn’t expect earthquakes. :’)

[SunkenCiv]

Thanks BenLurkin! Gotta be one of the most abstruse topic names, ever, on FR.

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[BenLurkin]

The wife wanted to paint the walls in the guest room abstruse.