Can the Fisk Conjecture be Explained by Rock Damage Around Explosions?

Taylor, Steven R.

doi:10.1785/0120080332

Cited by 6 publications

(5 citation statements)

References 13 publications

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“…They claim that contributions of damage to the radiation from earthquakes can be comparable to or larger than the contribution of moment release due to slip on earthquake faults. Material damage has long been recognized by explosion and earthquake seismologists as a potential source, and models for the seismic radiation have been developed over the years [e.g., Mal and Knopoff , 1967; Knopoff and Randall , 1970; Ashby and Sammis , 1990; Johnson and Sammis , 2001; Taylor , 2009]. Among the predictions of these models is the fact that source medium damage can radiate waves as volumetric, double couple, and compensated linear vector dipole (CLVD) body force systems.…”

Section: Introductionmentioning

confidence: 99%

The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions

Patton

Taylor

2011

J. Geophys. Res.

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[1] Classical explosion source theory relates isotropic seismic moment to the steady state level of the reduced displacement potential. The theoretical isotropic moment for an incompressible source region M t is proportional to cavity volume V c created by pressurization of materials around the point of energy release. Source medium damage due to nonlinear deformations caused by the explosion will also induce volume change V d and radiate seismic waves as volumetric, double-couple, and compensated linear vector dipole (CLVD) body force systems. A new source model is presented where K is a relative measure of moment M CLVD with respect to the net moment from volumetric sources V c and V d . K values from moment tensor inversions steadily decrease from ∼2.5 at lower yields to ∼1.0 for the highest-yield shots on Pahute Mesa. A value of 1.0 implies M CLVD = 0 and, by inference, small V d . We hypothesize that the extent to which damage adds (or subtracts) volumetric moment is controlled by material properties and dynamics of stress wave rebound, shock wave interactions with the free surface, gravitational unloading, and slapdown of spalled near-surface layers. This hypothesis is tested by comparing measurements of isotropic momentM I with estimates of M t based on V c scaling relationships and velocity-density models. The results support the hypothesis and the conclusion thatM I represents the "apparent explosion moment" since it has contributions from direct effects due to cavity formation and indirect effects due to material damage. Implications for yield estimation usingM I are discussed in general and for the North Korean tests.Citation: Patton, H. J., and S. R. Taylor (2011), The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions,

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Section: Introductionmentioning

confidence: 99%

The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions

Patton

Taylor

2011

J. Geophys. Res.

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“…The physical controls on explosion‐induced S wave spectra remain debated. If a difference in source spectra explains the observed frequency dependence of P / S ratios, the physical cause may be rooted in the different P and S wave elastic length scales of sensitivity to near‐source rock damage (Taylor, 2009). However, a variety of complicated and locally specific effects such as spall and free‐surface topographic scattering are thought to influence explosion‐induced S wave spectra (e.g., Patton & Taylor, 1995; Xie & Lay, 1994).…”

Section: Discussionmentioning

confidence: 99%

Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios

2020

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Explosions and earthquakes are effectively discriminated by P/S amplitude ratios for moderate magnitude events (M ≥ 4) observed at regional to teleseismic distances (≥200 km). It is less clear if P/S ratios are effective explosion discriminants for lower magnitudes observed at shorter distances. We report new tests of P/S discrimination using a dense seismic array in a continental volcanic arc setting near Mount St. Helens, with 23 single-fired borehole explosions (M L 0.9-2.3) and 406 earthquakes (M L 1-3.3). The array provides up to 95 three-component broadband seismographs, and most source-receiver distances are <120 km. Additional insight is provided by~3,000 vertical component geophone recordings of each explosion. Potential controls on local distance P/S ratios are investigated, including frequency range, distance, magnitude, source depth, number of seismographs, and site effects. A frequency band of about 10-18 Hz performs better than lower or narrower bands because explosion-induced S wave amplitudes diminish relative to P for higher frequencies. Source depth and magnitude exhibited weak influences on P/S ratios. Site responses for earthquakes and explosions are correlated with each other and with shallow crustal V p and V s from traveltime tomography. Overall, the results indicate high potential for local distance P/S explosion discrimination in a continental volcanic arc setting, with ≥98% true positives and ≤6.3% false positives when using the array median from ≥16 stations. Performance is reduced for smaller arrays, especially those with ≤4 stations, thereby emphasizing the importance of array data for discrimination of low magnitude explosions. Plain Language Summary Methods to remotely classify seismic sources as either shear-slip earthquakes or shallow subsurface explosions are important geophysical tools. They are used for investigations of anthropogenic processes such as underground nuclear explosion tests and mining activity as well as to obtain pure catalogs of tectonic and volcanic earthquakes. The ratio of compressional (P) wave amplitude to shear (S) wave amplitude is effective for classifying large earthquakes and explosions observed hundreds to thousands of kilometers away. Application of such methods at local distances is a topic of growing interest because smaller magnitude sources are only observed at close distances. We tested influences on P/S amplitude ratios and their effectiveness for source discrimination using a data set of tectonic and volcanic earthquakes and controlled shallow borehole explosions near Mount St. Helens. Most observations were within 120 km. We found that use of high frequencies and array-median statistics is largely effective for source discrimination in this setting, successfully classifying 100% of explosions while falsely attributing about 5% of earthquakes to explosions. Variability of P/S ratios across the seismic array has a highly similar pattern for explosions and earthquakes and that pattern appears to be controlled by the seismic velocity structure of...

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“…Fisk (2006Fisk ( , 2007 has postulated that explosion P/S values can be modeled using the Mueller-Murphy P-wave model where the S-wave are calculated by scaling the S-wave corner frequency by the ratio of the S to P-wave velocity. Taylor (2009) has proposed that this S-wave corner frequency effect might be due to rock damage from the explosion and that it might persist even for very overburied events. In Figure 7, we show that using this explosion model predicts that the P/S value for Hellum-1 is expected to be much lower at 2-4 and 4-6 Hz than the other PNEs measured here.…”

Section: Discussionmentioning

confidence: 99%

Testing Event Discrimination over Broad Regions using the Historical Borovoye Observatory Explosion Dataset

Pasyanos

Ford

Walter

2012

Pure Appl. Geophys.

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We test the performance of high-frequency regional P/S discriminants to differentiate between earthquakes and explosions at test sites and over broad regions using a historical dataset of explosions recorded at the Borovoye observatory in Kazakhstan. We compare these explosions to modern recordings of earthquakes at the same location. We then evaluate the separation of the two types of events using the raw measurements and those where the amplitudes are corrected for 1-D and 2-D attenuation structure. We find that high-frequency P/S amplitudes can reliably identify earthquakes and explosions and that the discriminant is applicable over broad regions as long as propagation effects are properly accounted for. Lateral attenuation corrections provide the largest improvement in the 2-4 Hz band, the use of which may allow us to examine smaller, distant events that have lower signal-to-noise at higher frequencies. We also find variations in P/S ratios among the three main nuclear testing locations within the Semipalatinsk Test Site which, due to their nearly identical paths to BRVK, must be a function of differing geology and emplacement conditions.

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Can the Fisk Conjecture be Explained by Rock Damage Around Explosions?

Cited by 6 publications

References 13 publications

The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions

The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions

Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios

Testing Event Discrimination over Broad Regions using the Historical Borovoye Observatory Explosion Dataset

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