Dynamic triggering of high‐frequency bursts by strong motions during the 2004 Parkfield earthquake sequence

Fischer, A.; Peng, Zhigang; Sammis, Charles G.

doi:10.1029/2008gl033905

Cited by 31 publications

(35 citation statements)

References 28 publications

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“…Second, the stress perturbation associated with the P wave is usually considered to be too small to cause much dynamic triggering at large distances. Recently, Fischer et al [2008a, 2008b] reported P wave‐triggered high‐frequency bursts in the near field during 1999 Mw 7.6 Chi‐Chi, Taiwan, earthquake and the 2004 Mw 6.0 Parkfield earthquake. They estimated a triggering threshold of ∼1 kPa.…”

Section: Discussionmentioning

confidence: 99%

Complex nonvolcanic tremor near Parkfield, California, triggered by the great 2004 Sumatra earthquake

et al. 2009

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[1] In several instances, the passing surface waves from large earthquakes have ignited nonvolcanic tremor (NVT) on major faults. Still, the mechanism of tremor and its reaction to the dynamic stressing from various body and surface waves is poorly understood. We examine tremor near Parkfield, California, beneath the San Andreas fault triggered by the Mw 9.2, 2004 Sumatra earthquake. The prolonged shaking produces the richest and the most varied observations of dynamically triggered tremor to date. The tremor appears in at least three distinct locations and shows activity pulsing with encouraging stress, as has been observed in other cases. The greatest amount of triggering and tremor modulation accompanies the long-period Love waves. Rayleigh waves, on the other hand, appear to be less effective in exciting tremor sources. Also, at times, the tremor stops before the surface waves are complete, at other times it continues quivering after the waves have passed. While tremor is found to be sensitive to small stress changes, there are times when stresses of comparable magnitudes do not trigger noticeable tremor. Some tremors in this NVT sequence appear to be associated with the passage of P waves, which is unusual and surprising given the small stresses they impart.

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Section: Discussionmentioning

confidence: 99%

Complex nonvolcanic tremor near Parkfield, California, triggered by the great 2004 Sumatra earthquake

et al. 2009

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“…There is direct evidence of brittle co‐seismic failure: small earthquakes in the shallow subsurface during shaking [ Fischer et al , 2008a, 2008b; Fischer and Sammis , 2009]. The largest of these events may cause brief extreme dynamic acceleration [ Aoi et al , 2008; Sleep and Ma , 2008].…”

Section: Stresses Within Seismically Damaged Regolithmentioning

confidence: 99%

Seismically damaged regolith as self-organized fragile geological feature

Sleep

2011

Geochem. Geophys. Geosyst.

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[1] The S-wave velocity in the shallow subsurface within seismically active regions self-organizes so that typical strong dynamic shear stresses marginally exceed the Coulomb elastic limit. The dynamic velocity from major strike-slip faults yields simple dimensional relations. The near-field velocity pulse is essentially a Love wave. The dynamic shear strain is the ratio of the measured particle velocity over the deep S-wave velocity. The shallow dynamic shear stress is this quantity times the local shear modulus. The dynamic shear traction on fault parallel vertical planes is finite at the free surface. Coulomb failure occurs on favorably oriented fractures and internally in intact rock. I obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock extending all the way to the surface. The imposed dynamic shear strain in stiff rock causes Coulomb failure at shallow depths and leaves cracks in it wake. Cracked rock is more compliant than the original intact rock. Cracked rock is also weaker in friction, but shear modulus changes have a larger effect. Each subsequent event causes additional shallow cracking until the rock becomes compliant enough that it just reaches Coulomb failure over a shallow depth range of tens to hundreds of meters. Further events maintain the material at the shear modulus as a function where it just fails. The formalism provided in the paper yields reasonable representation of the S-wave velocity in exhumed sediments near Cajon Pass and the San Fernando Valley of California. A general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking. This process causes transient changes in S-wave velocity, but not strong nonlinear attenuation of seismic waves. Wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock.Components: 8800 words, 12 figures.

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“…Also from , sudden failure of shallow rock with a large stress drop will produce brief accelerations. Small events of this type result in brief pulses that can be studied by high‐pass filtering [ Fischer et al ., , Fischer and Sammis , ]. Large events of this type are a likely cause of observed brief accelerations of greater than 1 g [ Aoi et al ., ; Sleep and Ma , ].…”

Section: Shear Waves Near the Earth's Surfacementioning

confidence: 99%

Nonlinear attenuation of S-waves and Love waves within ambient rock

Sleep

Erickson

2014

Geochem. Geophys. Geosyst.

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We obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate without strong nonlinear attenuation. During each event, the shaking episode cracks the stiff, shallow rock. Over multiple events, this repeated damage in the upper few hundred meters leads to self-organization of the shear modulus. Dynamic strain is PGV divided by phase velocity, and dynamic stress is strain times the shear modulus. The frictional yield stress is proportional to depth times the effective coefficient of friction. At the eventual quasi-steady self-organized state, the shear modulus increases linearly with depth allowing inference of past typical PGV where rock over the damaged depth range barely reaches frictional failure. Still greater future PGV would cause frictional failure throughout the damaged zone, nonlinearly attenuating the wave. Assuming self-organization has taken place, estimated maximum past PGV within Greater Los Angeles Basins is 0.4-2.6 m s 21. The upper part of this range includes regions of accumulating sediments with low S-wave velocity that may have not yet compacted, rather than having been damaged by strong shaking. Published numerical models indicate that strong Love waves from the San Andreas Fault pass through Whittier Narrows. Within this corridor, deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double PGV of Love waves reaching Downtown Los Angeles.

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Dynamic triggering of high‐frequency bursts by strong motions during the 2004 Parkfield earthquake sequence

Cited by 31 publications

References 28 publications

Complex nonvolcanic tremor near Parkfield, California, triggered by the great 2004 Sumatra earthquake

Complex nonvolcanic tremor near Parkfield, California, triggered by the great 2004 Sumatra earthquake

Seismically damaged regolith as self-organized fragile geological feature

Nonlinear attenuation of S-waves and Love waves within ambient rock

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