Rocky Mountain Geophysics, Inc.

Los Alamos, NM, United States

Rocky Mountain Geophysics, Inc.

Los Alamos, NM, United States
SEARCH FILTERS
Time filter
Source Type

Taylor S.R.,Rocky Mountain Geophysics, Inc. | Arrowsmith S.J.,Los Alamos National Laboratory | Anderson D.N.,Los Alamos National Laboratory
Bulletin of the Seismological Society of America | Year: 2010

We present a methodology for the detection of small, impulsive signal transients using time-frequency spectrograms closely related to the emerging field of scan statistics. In local monitoring situations, single-channel detection of small explosions can be difficult due to the complicated nature of the local noise field. Small, impulsive signals are manifest as vertical stripes on spectrograms and are enhanced on grayscale representations using vertical detection masks. Bitmap images are formed where pixels above a defined threshold are set to one. A short-duration large bandwidth signal will have a large number of illuminated bits in the column corresponding to its arrival time. We form the marginal distribution of bit counts as a function of time, ni, by summing columnwise over frequency. For each time window we perform a hypothesis test, H0: signal + noise, by defining a probability model expected when a signal is present. This model is Bernoulli for signal versus no signal with probability of signal = p1. We assume that ni follows the binomial distribution and compute a probability of detection (represented as a p value) for a given p1.We apply the spectrogram detector to 1 hr of single-channel acoustic data containing a signal from a 1 lb chemical surface explosion recorded at 3.1 km distance and compare performance with a short-term average to long-term average (STA/LTA) detector. Both detectors are optimized through grid search and successfully detect the acoustic arrival from the 1 lb explosion. However, 70% more false detections are observed for STA/LTA than for the spectrogram detector. At great range, attenuation properties of the earth reduce the effectiveness of the spectrogram detector relative to STA/LTA. Data fusion techniques using multiple channels from a network are shown to reduce the number of false detections.


Arrowsmith S.J.,Los Alamos National Laboratory | Taylor S.R.,Rocky Mountain Geophysics, Inc.
Journal of the Acoustical Society of America | Year: 2013

A methodology for the combined acoustic detection and discrimination of explosions, which uses three discriminants, is developed for the purpose of identifying weak explosion signals embedded in complex background noise. By utilizing physical models for simple explosions that are formulated as statistical hypothesis tests, the detection/discrimination approach does not require a model for the background noise, which can be highly complex and variable in practice. Fisher's Combined Probability Test is used to combine the p-values from all multivariate discriminants. This framework is applied to acoustic data from a 400 g explosion conducted at Los Alamos National Laboratory. © 2013 U.S. Government.


Taylor S.R.,Rocky Mountain Geophysics, Inc. | Arrowsmith S.J.,Los Alamos National Laboratory | Anderson D.N.,Los Alamos National Laboratory
Journal of the Acoustical Society of America | Year: 2013

A method for acoustic detection of small explosions at local distances is presented combining a matched filter with a p-value representing the conditional probability of detection. Because the physics of signal generation and propagation for small, locally recorded acoustic signals from small explosions is well understood, the single hypothesis to be tested is a signal corrupted by additive noise. A simple analytical signal representation is used where a known signal is assumed with parameters to be determined. The advantage of the approach is that the detector can be combined with other detectors that measure different signal characteristics all under the same unifying hypothesis. © 2013 U.S. Government.


Patton H.J.,Los Alamos National Laboratory | Taylor S.R.,Rocky Mountain Geophysics, Inc.
Journal of Geophysical Research: Solid Earth | Year: 2011

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 Mt is proportional to cavity volume Vc 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 Vd 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 MCLVD with respect to the net moment from volumetric sources Vc 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 MCLVD = 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 moment M̂I with estimates of Mt based on Vc scaling relationships and velocity-density models. The results support the hypothesis and the conclusion that M̂I 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 using M̂I are discussed in general and for the North Korean tests. Copyright 2011 by the American Geophysical Union.


Taylor S.R.,Rocky Mountain Geophysics, Inc. | Patton H.J.,Los Alamos National Laboratory
Geophysical Research Letters | Year: 2013

Effects of rock damage on teleseismic mb are investigated with P wave synthetic seismograms using a moment dipole Mzz as the equivalent elastic model for damage around buried explosions. Two manifestations of late-time damage, cavity rebound and bulking from block rotations, are represented by model decompositions into compensated linear vector dipole and monopole sources, respectively. For high-velocity media, P waves from damage destructively interfere with those from the explosion. This interference reduces the rate at which mb yield scales for a pure monopole source and provides a physical basis for observed scaling in hard rock, mb~0.75 log [yield]. For over-buried explosions, such as the North Korean tests, P waves from damage are weaker, and higher scaling rates are expected than explosions conducted under standard containment conditions. Our results highlight a cautionary note of transporting the same mb-log[yield] relation between test sites to estimate yield when source phenomenology is likely to be very different. © 2013. American Geophysical Union. All Rights Reserved.


Taylor S.R.,Rocky Mountain Geophysics, Inc.
Bulletin of the Seismological Society of America | Year: 2011

This paper describes a statistical methodology for earthquake/explosion discrimination using two-dimensional (2D) grids (frequency of S against frequency of P) of regional P/S ratios. A method similar to that of scan statistics is developed by applying a counting rule on an N-length bitmap image of the 2D plots. An average density of bits is computed for explosions in the training set; it is assumed that each bitmap cell represents an independent sample taken from a Bernoulli process. A hypothesis test HO: explosion is designed, and a p value (a statistical measure) indicating the degree of membership of a new event to the explosion population is computed. A statistical method is presented that allows construction of p values under the null hypothesis that the event in question is an explosion. The field of view is the lower-right triangular corner plot for P/S ratios closely related to the high-frequency P to low-frequency S discriminant. The plot is converted to a bit map, and bits are summed and treated as a Bernoulli random variable. Using a set of calibration data, the background density of bits for explosions can be estimated and used to compute p values for new events. Importantly, the p values from the 2D P/S ratios can be naturally combined with other p values from other discriminants constructed under the same hypothesis to form a multivariate discriminant as in Anderson et al. (2007).


Anderson D.N.,Los Alamos National Laboratory | Patton H.J.,Los Alamos National Laboratory | Taylor S.R.,Rocky Mountain Geophysics, Inc. | Bonner J.L.,Weston Geophysical Corp. | Selby N.D.,Atomic Weapons Establishment
Pure and Applied Geophysics | Year: 2014

The Comprehensive Nuclear-Test-Ban Treaty (CTBT), a global ban on nuclear explosions, is currently in a ratification phase. Under the CTBT, an International Monitoring System (IMS) of seismic, hydroacoustic, infrasonic and radionuclide sensors is operational, and the data from the IMS is analysed by the International Data Centre (IDC). The IDC provides CTBT signatories basic seismic event parameters and a screening analysis indicating whether an event exhibits explosion characteristics (for example, shallow depth). An important component of the screening analysis is a statistical test of the null hypothesis H 0: explosion characteristics using empirical measurements of seismic energy (magnitudes). The established magnitude used for event size is the body-wave magnitude (denoted m b) computed from the initial segment of a seismic waveform. IDC screening analysis is applied to events with m b greater than 3.5. The Rayleigh wave magnitude (denoted M S) is a measure of later arriving surface wave energy. Magnitudes are measurements of seismic energy that include adjustments (physical correction model) for path and distance effects between event and station. Relative to m b, earthquakes generally have a larger M S magnitude than explosions. This article proposes a hypothesis test (screening analysis) using M S and m b that expressly accounts for physical correction model inadequacy in the standard error of the test statistic. With this hypothesis test formulation, the 2009 Democratic Peoples Republic of Korea announced nuclear weapon test fails to reject the null hypothesis H 0: explosion characteristics. © 2013 Springer Basel (outside the USA).


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 999.80K | Year: 2011

One main issue associated with nuclear explosion monitoring is the paucity of accurate Ground Truth (GT) data used for the calibration of regional seismic networks, particularly in aseismic regions. Location accuracy of U.S. monitoring and the International Monitoring System provided for by the Comprehensive Test Ban Treaty could be significantly improved with accurate GT data from large mines distributed across the globe. We are developing a Ground-Truth Monitoring System (GTMS) consisting of an inexpensive, lightweight smart sensor unit that can be mailed to and emplaced near large mining regions. The GTMS can operate autonomously and automatically transmit accurate information regarding explosion epicenter, origin time and magnitude. Because of inexpensive ORBCOMM satellite two-way communications, we are developing an accompanying Ground-Truth Processing Center (GTPC) that can be used to improve calibration and processing over the course of a deployment providing accurate ground-truth data within the operational constraints provided by the intended users. In Phase I, we have demonstrated the feasibility of developing a Ground-Truth Monitoring System in terms of hardware design and software (signal processing) algorithms. It appears feasible that the system will meet specified operational goals of ground-truth accuracy, low cost, low power consumption, and autonomous operation without any human intervention. A prototype hardware system using seismic geophones, MEMS sensors and acoustic microphones is already being developed along with a processing framework. We have also developed the concept of a Ground Truth Processing Center (GTPC) which can be used to improve calibration parameters over the course of a deployment. Probably the only constraint that will be difficult to meet is the cost and weight. Our estimates for minimum cost and the total weight of the system is going to be approximately $1500, and 3 lbs, respectively including enclosure, batteries and sensors. In Phase II, a prototype system will be built and deployed at mines in different geophysical regions. We will focus on algorithm improvement and automation for the Ground-Truth Monitoring System that can be implemented within hardware and processing constraints. Because the GTMS will have two-way communication, we propose to develop a Ground-Truth Processing Center (GTPC) that can be used to adaptively improve ground-truth accuracy over the duration of a deployment. The Ground-Truth Monitoring System will have many applications besides nuclear explosion monitoring. Because of our flexible processing system, algorithms can be adapted to locate and track micro-earthquakes caused by injection wells used for carbon sequestration, oil and gas recovery, geothermal plants and hydro-fracturing operations. The system will also be useful for border security and perimeter monitoring of facilities as well as underground mine safety systems. For many applications, our business model actually becomes similar to that of a home security service where our GTPC is used to improve monitoring capabilities as well as provide high-confidence alerts.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.99K | Year: 2010

Accurate seismo-acoustic source location is one of the fundamental aspects of U.S. nuclear explosion monitoring and for verification of a Comprehensive Test Ban Treaty (CTBT). Critical to improved location is the compilation of ground truth data sets for which origin time and location are accurately known. We propose to build an inexpensive, ground truth smart sensor that could be placed in close proximity (< 5 km) to mining regions that would greatly aid in development of ground truth datasets thereby improving U.S. nuclear explosion monitoring capabilities. The overall objective is to build a compact, self-contained, inexpensive smart sensor seismo/acoustic system that can be placed in mining regions for nuclear explosion monitoring ground truth development efforts. Our approach is to analyze available locally-recorded mine explosions in order to develop algorithms and associated hardware to meet operational goals necessary for transmittal of accurate ground truth data. The hardware and algorithms developed as part of our Phase I and II study can be migrated to the processor for applications such as border security, facility monitoring, and measuring ground motion from surface mines, early earthquake alert warning systems, deep underground coal mine safety among others. Seismic, acoustic, nuclear explosion monitoring, smart sensors, ground truth, mining regions Rocky Mountain Geophysics, Inc. will develop a seismo/acoustic smart sensor system to be used to transmit accurate ground truth information (location, origin time, magnitude) from mining regions to improve U.S. nuclear explosion monitoring capabilities. Commercial Applications and Other Benefits:The system will be compact, inexpensive, simple to deploy and capable of autonomous operation for periods of up to six months.


Grant
Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase I | Award Amount: 70.00K | Year: 2010

We propose to conduct a feasibility study for utilizing broadband sampling of the diffusive noise field in a dynamic environment. In ambient noise studies, the ability to resolve a wavefield is proportional to its time-bandwidth (TB) product. In a dynamic environment such as in the atmosphere or ocean, the nature of the impinging wave field is changing rapidly so that only short time segments can be used to model the ambient wave field thereby reducing the TB product. One way to counter the effect of a reduced time window is to increase the bandwidth of measurement. Our approach is to broaden the frequency spectrum used to characterize diffusive noise fields in dynamic environments by addition of Intensity Level Differences (ILD) caused by diffraction around a shadowing object to the more commonly used interferometric phase delay methods. Diffraction around a shadowing object can create acoustic bright spots that are easily detected. As an experimental test, we will use ambient noise data from existing infrasonic arrays and characterize the dynamic wavefield using passive interferometry and spatial gradiometry techniques. For spatial gradient techniques, the required sensor footprint is smaller and the wavefield can be mapped at higher resolution at closer ranges.

Loading Rocky Mountain Geophysics, Inc. collaborators
Loading Rocky Mountain Geophysics, Inc. collaborators