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 ten or more reports in ten minutes; 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 (SQM) through the earth, although there is no direct confirmation from other phenomenologies.Comment: 23 pages, 9 figures, one previously described event eliminated, extensive examination of the second event as a possible association of random reports, additional analysis of the data set, search algorithms, and waveform

Evaluation of Short-Period, Near-Regional M_s 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

Investigation of an Unusually Shallow Earthquake Sequence in Mogul, NV from a Discrimination Perspective

Distinction between very shallow (1-4 km deep) earthquakes and underground nuclear explosions remains an important issue in discrimination research. This is because very shallow earthquakes are seldom well-recorded and documented. As a consequence, their source parameters, scaling and their local and regional propagation characteristics are not well understood. Thus, unlike for deeper events, the effectiveness of the discrimination algorithms when applied to unusually shallow earthquakes has been only rarely determined. The primary objective of this study is a detailed investigation of a sequence of earthquakes that occurred during 2008 west of Reno, Nevada, in Mogul. This sequence consisted of over 1700 earthquakes with ML of 1.0 or greater, concentrated in depth between 1 and 4 km and ranging in magnitude up to Mw 5.0 (the “main shock”). Preliminary analyses of the main shock have revealed uncharacteristically high amplitude near-field ground motions and uncharacteristically rapid attenuation with distance, which could affect the magnitude estimates and the discrimination metrics. For our investigations, we use a unique broadband and strong-motion recording database, from stations as close as 1 km from the epicenter of the main shock and most of the smaller events. We have organized our study in four tasks: First, our investigations started by building a detailed shallow event database. In addition to available public domain information on very shallow event discrimination analysis, the database includes near-field and seismic network recordings of all the ML\u3e1.0 Mogul, Nevada earthquakes located by the Nevada Seismological Laboratory; mining explosions (ML\u3e2.0) and crustal earthquakes (ML\u3e2.5) in the in the Reno-Carson City, NV, area; the waveforms from the 1993 Rock Valley sequence (depth \u3c 4 km, mb≤4.3) and waveforms from the 2007 Crandall Canyon mine collapse, (ML 3.9). The objectives of the second task are to analyze the stress drop and radiated energy of the main shock, principal foreshocks, and principal aftershocks as well as to investigate the source scaling of the Mogul sequence. We will estimate source parameters (moment, corner frequency, stress drop) for ML ≥ 3.5 Mogul events using three related methods: 1) Spectral measurements; 2) Empirical Green\u27s Functions and 3) Measurements of Lg/Sn coda envelopes. Third, we will investigate the effect of source depth on P and S spectra and spectral ratios, signal complexity, and the mb versus Ms discriminant. Fourth, we will attempt to understand the origin and nature of the near-source attenuation and its effect on magnitude estimates and energy content-related discriminant performance. We will compare our results to other very shallow earthquake sequences, induced seismicity and nuclear explosions results