Eugene Herrin

Thermal Constraints on Earthquake Depths in California

The high-quality databases for California seismicity (from the Southern and Northern California Earthquake Centers) and an extensive compilation of thermal measurements in California are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone. The base of this zone, below which only a small percentage of crustal earthquakes occur, is termed the “cutout depth,” and it is at or near the brittle-ductile transition in the crust. Based on laboratory deformation studies, this transition should be temperature, strain rate, lithology, and stress-state dependent. In this study, qualitative comparisons between the heat flow in California and earthquake hypocentral distributions show first that, as expected, earthquake cutout depths are inversely related to heat flow. Second, the epicentral distributions tend to parallel thermal transitions. This correlation is probably related to stress concentrations in these locations. An ancillary observation is that the cooler western Mojave block in southern California appears to be behaving similarly to the Tibetan indenter block in Asia, as faults tend to go around it into areas of higher heat flow where the seismogenic zone is thinner and the crust may be weaker, and it is pushed toward (and under) the southern cold Sierra Nevada block. Third, to quantitatively compare the data sets, temperatures for the seismicity cutout depth in California were calculated using the steady-state, 1D heat conduction equation, with the variables based on published values for heat flow, heat generation, and thermal conductivity. The analysis was restricted to profiles along which the heat flow and earthquake databases were constrained, which allowed the error in the temperature calculation to be determined using Monte Carlo simulations. The results show that two distinct ranges of temperatures (dependent upon location) describe the cutout depth ( D 99%) of seismicity for California: 450 ± 50°C and 260 ± 40°C. The 450 ± 50°C cutout depth temperature is most widespread geographically, occurs within many provinces, and is higher than the frequently referenced temperature of 300 ± 50°C for the brittle-ductile transition. The lower temperature (260°C) seems to be restricted to provinces where the heat flow is near or below 50 mW m-2, such as the Mojave block and Sierra Nevada. The differences in these cutout temperatures suggest that additional factors, such as strain rate, stress regime, and/or lithology, may contribute to the seismicity cutout depth. Fourth, along a profile with significant seismic activity and a 450°C cutout temperature, the envelope for the maximum energy released by earthquakes falls at or below the 300°C isotherm. Detailed characterization of the heat flow and earthquake synergy in this manner furthers the understanding of the earthquake process and can aid in the estimation of the maximum depth of rupture for great earthquakes, particularly in areas of low seismicity, thus reducing uncertainties in hazard calculations. Manuscript received 26 February 2003.

Seismic search for strange quark nuggets

Bounds on masses and abundances of Strange Quark Nuggets (SQNs) are inferred from a seismic search on Earth. Potential SQN bounds from a possible seismic search on the Moon are reviewed and compared with Earth capabilities. Bounds are derived from the data taken by seismometers implanted on the Moon by the Apollo astronauts. We show that the Apollo data implies that the abundance of SQNs in the region of 10 kg to 1 ton must be at least an order of magnitude less than would saturate the dark matter in the solar neighborhood.

High-Altitude Infrasound Calibration Experiments

H. E Bass, E. T Herrin, P. Golden, R. Woodward, D. Drob, M. A H Hedlin, C. De Groot-Hedlin, K. Walker, M. Garces , C. Szuberla and R. Whitaker The University of Mississippi NCPA, 1 Coliseum Drive, University, MS 38677, USA Southern Methodist University, P. O. Box 750395, Dallas, TX 75275, USA Incorporated Research Institutions for Seismology, 1200 New York Avenue, NW, Suite 800, Washington, DC 20005, USA Naval Research Laboratory, Space Science Division, 4555 Overlook Avenue, Washington, DC 20375, USA University of San Diego California, Scripps Institute of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093, USA Infrasound Laboratory, University of Hawaii, 73-4460 Queen Kaahumanu Highway #119, Kailua-Kona, HI 96740, USA University of Alaska, 903 Koyukuk Drive, Fairbanks, AK 99775, USA Los Alamos National Laboratory, EES-2 MS J577, Los Alamos, NM 87545, USA

Unexplained Sets of Seismographic Station Reports and A Set Consistent with a Quark Nugget Passage

In 1984 Edward Witten proposed that an extremely dense form of matter composed of up, down, and strange quarks may be stable at zero pressure (Witten, 1984). Massive nuggets of such dense matter, if they exist, may pass through the Earth and be detectable by the seismic signals they generate (de Rujula and Glashow, 1984). With this motivation we investigated over 1 million seismic data reports to the U.S. Geological Survey for the years 1990-1993 not associated with epicentral sources. We report two results: (1) with an average of about 0.16 unassociated reports per minute after data cuts, we found a significant excess over statistical expectation for sets with 10 or more reports in 10 min; and (2) in spite of a very small a priori probability from random reports, we found one set of reports with arrival times and other features appropriate to signals from an epilinear source. This event has the properties predicted for the passage of a nugget of strange quark matter through the Earth, although there is no direct confirmation from other phenomenologies. Manuscript received 20 June 2002.

Evaluation of Short-Period, Near-Regional Ms Scales for the Nevada Test Site

Surface wave magnitude (M_s) estimation for small events recorded at near-regional distances will often require a magnitude scale designed for Rayleigh waves with periods less than 10 sec. We have examined the performance of applying two previously published M_s scales on 7-sec Rayleigh waves recorded at distances less than 500 km. First, we modified the Marshall and Basham (1972) M_s scale, originally defined for periods greater than 10 sec, to estimate surface wave magnitudes for short-period Rayleigh waves from earthquakes and explosions on or near the Nevada Test Site. We refer to this modification as ^(M+B) M_s(7), and we have used short-period, high-quality dispersion curves to determine empirical path corrections for the 7-sec Rayleigh waves. We have also examined the performance of the Rezapour and Pearce (1998) formula, developed using theoretical distance corrections and surface wave observations with periods greater than 10 sec, for 7-sec Rayleigh waves ^(R+P) (M_S(7)) as recorded from the same dataset. The results demonstrate that both formulas can be used to estimate M_s for nuclear explosions and earthquakes over a wider magnitude distribution than is possible using conventional techniques developed for 20-sec Rayleigh waves. These M_s(7) values scale consistently with other Ms studies at regional and teleseismic distances with the variance described by a constant offset; however, the offset for the ^(M+B) M_s(7) estimates is over one magnitude unit nearer the teleseismic values than the ^(R+P) M_s(7) estimates. Using our technique, it is possible to employ a near-regional single-station or sparse network to estimate surface wave magnitudes, thus allowing quantification of the size of both small earthquakes and explosions. Finally, we used a jackknife technique to determine the false-alarm rates for the ^(M+B) M_s(7)-m_b discriminant for this region and found that the probability of misclassifying an earthquake as an explosion is 10%, while the probability of classifying an explosion as an earthquake was determined to be 1.2%. The misclassification probabilities are slightly higher for the ^(R+P) M_s(7) estimates. Our future research will be aimed at examining the transportability of these methods.

High‐altitude infrasound calibration experiments

At the 152nd Meeting of the Acoustical Society of America, Andre and Bass reported an infrasound experiment conducted at White Sands Missile Range during the 2005‐2006 time frame. The experiment consisted of exploding a 22.4 kg charge at altitudes from 31.3 km to 49.6 km then recording the waveforms at 30 infrasound arrays (not all at the same time) at distances up to 1200 km from the source. The analysis is not yet complete but some preliminary observations have been reported in the most recent issue of Acoustics Today. This talk will summarize the findings published in Acoustics Today and offer suggestions to others who might want to access and analyze the data.

Properties of pressure fluctuations in an atmospheric boundary layer

From experimental data it is shown that there is a relationship between measured wind speed and associated micropressure levels. It is also shown that turbulent eddies associated with the wind vanish within distances of five to six times their size, and that these eddies exhibit normal dispersion. These results confirm, at the atmospheric scales, results previously observed only in model experiments.

Millimeter-Wave Signature of Strange Matter Stars

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they consist of neutron star matter or strange quark matter (SQM). However, few mechanisms for distinguishing between these two possibilities have been proposed. The purpose of this Letter is to show that a strange star (one made of SQM) will have a vibratory mode with an oscillation frequency of approximately 250 GHz (millimeter wave). This mode corresponds to motion of the center of the expected crust of normal matter relative to the center of the strange quark core, without distortion of either. Radiation from currents generated in the crust at the mode frequency would be an SQM signature. We also consider effects of stellar rotation, estimate power emission and signal-to-noise ratio, and discuss briefly the particularly important, but unsolved, question of possible mechanisms for exciting the mode.

Infrasound propagation in the zone of silence

Two controlled source experiments were conducted in Nevada in 2006 and 2007 to study infrasound signal propagation at distances less than 300 km from the source. In 2006 three temporary infrasound arrays were deployed at distances of 76, 108, and 157 from the source. In 2007 the site at 157 km was reoccupied, and data was also recorded at 288 km from the source. Interesting results were derived from the travel time analysis. In 2006 the site at 76 km recorded both tropospheric and stratospheric arrivals, while at 108 and 157 km only stratospheric arrivals were recorded. In 2007 the site at 157 km recorded both tropospheric and stratospheric arrivals, while at 288 km both stratospheric and thermospheric arrivals were recorded. Atmospheric modeling with the InfraMAP software failed to predict returning rays or pressure levels similar to the observed data. Because of the large amplitude variations we attempt to estimate the yields of the explosions using the predominant frequency content of the signals. The ...

Seismic Search for Strange Quark Matter

We briefly review the status of strange quark matter and the capabilities of seismic networks for detecting nuggets of strange quark matter that pass through the Earth if an appreciable fraction of galactic halo dark matter is in the form of ton-sized nuggets. We describe progress to date in analyzing 13 years of seismic data and we note the possibility that new networks under development for verifying compliance with the recently negotiated Comprehensive Test Ban Treaty might be capable of contributing to detection of such nuggets.