70 Matching Results

Search Results

Advanced search parameters have been applied.

Earthquakes in California in 1890 and 1891

Description: A paper which records all of the shocks observed or felt on Mount Hamilton, and all of those reported to the Lick Observatory by letter; as well as newspaper reports of such earthquakes as occurred in the state during that year.
Date: 1892
Creator: Holden, Edward Singleton
Partner: UNT Libraries Government Documents Department

Earthquakes in California in 1893

Description: A report about recorded shock waves observed or felt on Mount Hamilton, and all those reported to the Lick Observatory by letter, as well as newspaper reports of such earthquakes that occurred in California during that year.
Date: 1894
Creator: Perrine, Charles D.
Partner: UNT Libraries Government Documents Department

Processed seismic motion records from earthquakes (1982--1993): Recorded at Scotty`s Castle, California

Description: As part of the contract with the US Department of Energy, Nevada Operations Office (DOE/NV), URS/John A. Blume & Associates, Engineers (URS/Blume) maintained a network of seismographs to monitor the ground motion generated by the underground nuclear explosions (UNEs) at the Nevada Test Site (NTS). The seismographs were located in the communities surrounding the NTS and the Las Vegas valley. When these seismographs were not used for monitoring the UNE generated motions, a limited number of seismographs were maintained for monitoring motion generated by other than UNEs (e.g. motion generated by earthquakes, wind, blast). Scotty`s Castle was one of the selected earthquake monitoring station. During the period from 1982 through 1993, numerous earthquakes with varied in magnitudes and distances were recorded at Scotty`s Castle. The records from 24 earthquakes were processed and included in this report. Tables 1 and 2 lists the processed earthquakes in chronological order and in the order of epicentral distances, respectively. Figure 1 shows these epicenters and magnitudes. Due to the potential benefit of these data for the scientific community, DOE/NV and the National Park Service authorize the release of these records.
Date: October 1, 1993
Creator: Lum, P.K. & Honda, K.K.
Partner: UNT Libraries Government Documents Department

Long-term seismic monitoring of the Roosevelt - Cove Fort KGRA's

Description: Earthquake monitoring of the Roosevelt-Cove Fort Hot Springs KGRA's was implemented by installation of three RF telemetered, vertical component, seismograph stations: CFU, MNU and RHU. These station sites were selected on the basis of proximity to the KGRA's, with respect to known earthquake activity determined in the microearthquake surveys. The three permanent stations form the basic long-term monitoring capability of the Roosevelt-Cove Fort KGRA's. The signals are FM transmitted to a collecting site near Milford then they are telephone-transmitted to the University of Utah campus for recording. The limitations of only three-stations precludes accurate hypocenter determinations but allows detection to a minimum threshold of about M-0.5 for close-in events. Locations can be determined for earthquakes of about M-0.7 or greater. Regional coverage of the south-central Utah KGRA's is supplemented by the use of other existing University of Utah stations to the east: MSU, PUU, and RFU. Together the six stations allow long-term detection of this geothermally active region.
Date: December 1, 1977
Creator: Smith, Robert B.
Partner: UNT Libraries Government Documents Department

Deep Structure Of Long Valley, California, Based On Deep Reflections From Earthquakes

Description: Knowledge of the deep structure of Long Valley comes primarily from seismic studies. Most of these efforts have focused on delimiting the top of the inferred magma chamber. We present evidence for the location of the bottom of the low velocity layer (LVL). Two other studies have provided similar information. Steeples and Iyer (1976) inferred from teleseismic P-wave delays that low-velocity material extends from 7 km depth to 25 to 40 km, depending on the velocities assumed. Luetgert and Mooney (1985) have examined seismic refraction data from earthquake sources and have identified a reflection that appears to be from the lower boundary of a magma chamber. They detected the reflection with a linear array of single component stations, and assuming it traveled in a vertical plane, matched the travel time and apparent velocity (6.3 km/sec) to deduce that it was a P-P reflection from within a LVL. We recorded a similar phase with a 2-dimensional array of three-component stations, and carried out a similar analysis, but utilized additional information about the travel path, particle motions and amplitudes to constrain our interpretation. Our data comes from a passive seismic refraction experiment conducted during August 1982. Fourteen portable seismograph stations were deployed in a network with approximately 5 km station spacing in the Mono Craters region north of Long Valley (Figure 1). The network recorded earthquakes located south of Long Valley and in the south moat. Three components of motion were recorded at all sites. The data represent one of the few times that three-component data has been collected for raypaths through a magma chamber in the Long Valley area.
Date: January 1, 1987
Creator: Zucca, J. J. & Kasameyer, P. W.
Partner: UNT Libraries Government Documents Department

Ultrasonic evaluation of flood gate tendons

Description: Our water resources infrastructure is susceptible to aging degradation just like the rest of this country`s infrastructure. A critical component of the water supply system is the flood gate that controls the outflow from dams.Long steel rods called tendons attach these radial gates to the concrete in the dam. The tendons are typically forty feet long and over one inch in diameter. Moisture may seep into the grout around the tendons and cause corrosion. Lawrence Livermore National Laboratory is working with the California Department of Water Resources to develop advanced ultrasonic techniques for nondestructively inspecting their tendons. A unique transducer was designed and fabricated to interrogate the entire tendon. A robust,portable unit was assembled that included a computer controlled data acquisition system and specialized data processing software to analyze the ultrasonic signals. This system was tested on laboratory specimens and is presently being fielded at two dam sites.
Date: October 1, 1997
Creator: Thomas, G. & Brown, A.
Partner: UNT Libraries Government Documents Department

Anomalous wave propagation across the South Caspian Basin

Description: The Caspian basin blocks the propagation of the regional seismic phase Lg and this has importance consequences for seismic discrimination in the Middle East. Intermediate period surface waves propagating across the basin are also severely affected. In a separate study we have developed a crustal model of the south Caspian basin and the surrounding region. The crust of the basin consists of 15-25 km of low velocity, highly attenuating sediments lying on high velocity crystalline crust. The Moho beneath the basin is at a depth of about 30 km as compared to about 50 km in the surrounding region. In this study we used an idealized rendition of this crustal model to compute hybrid normal mode finite difference synthetic seismograms to identify the features of the Caspian basin which lead to the seismic blockage. Of the various features of the basin, the thickness and attenuation of the sediments appear to be the dominant blocking mechanism.
Date: October 1, 1997
Creator: Priestly, K.; Patton, H.J. & Schultz, C.
Partner: UNT Libraries Government Documents Department

Optimized filtering of regional and teleseismic seismograms: results of maximizing SNR measurements from the wavelet transform and filter banks

Description: Development of a worldwide network to monitor seismic activity requires deployment of seismic sensors in areas which have not been well studied or may have from available recordings. Development and testing of detection and discrimination algorithms requires a robust representative set of calibrated seismic events for a given region. Utilizing events with poor signal-to-noise (SNR) can add significant numbers to usable data sets, but these events must first be adequately filtered. Source and path effects can make this a difficult task as filtering demands are highly varied as a function of distance, event magnitude, bearing, depth etc. For a given region, conventional methods of filter selection can be quite subjective and may require intensive analysis of many events. In addition, filter parameters are often overly generalized or contain complicated switching. We have developed a method to provide an optimized filter for any regional or teleseismically recorded event. Recorded seismic signals contain arrival energy which is localized in frequency and time. Localized temporal signals whose frequency content is different from the frequency content of the pre-arrival record are identified using rms power measurements. The method is based on the decomposition of a time series into a set of time series signals or scales. Each scale represents a time-frequency band with a constant Q. SNR is calculated for a pre-event noise window and for a window estimated to contain the arrival. Scales with high SNR are used to indicate the band pass limits for the optimized filter.The results offer a significant improvement in SNR particularly for low SNR events. Our method provides a straightforward, optimized filter which can be immediately applied to unknown regions as knowledge of the geophysical characteristics is not required. The filtered signals can be used to map the seismic frequency response of a region and may provide improvements ...
Date: July 15, 1997
Creator: Leach, R.R.; Schultz, C. & Dowla, F.
Partner: UNT Libraries Government Documents Department

Wavelet transform analysis of transient signals: the seismogram and the electrocardiogram

Description: In this dissertation I quantitatively demonstrate how the wavelet transform can be an effective mathematical tool for the analysis of transient signals. The two key signal processing applications of the wavelet transform, namely feature identification and representation (i.e., compression), are shown by solving important problems involving the seismogram and the electrocardiogram. The seismic feature identification problem involved locating in time the P and S phase arrivals. Locating these arrivals accurately (particularly the S phase) has been a constant issue in seismic signal processing. In Chapter 3, I show that the wavelet transform can be used to locate both the P as well as the S phase using only information from single station three-component seismograms. This is accomplished by using the basis function (wave-let) of the wavelet transform as a matching filter and by processing information across scales of the wavelet domain decomposition. The `pick` time results are quite promising as compared to analyst picks. The representation application involved the compression of the electrocardiogram which is a recording of the electrical activity of the heart. Compression of the electrocardiogram is an important problem in biomedical signal processing due to transmission and storage limitations. In Chapter 4, I develop an electrocardiogram compression method that applies vector quantization to the wavelet transform coefficients. The best compression results were obtained by using orthogonal wavelets, due to their ability to represent a signal efficiently. Throughout this thesis the importance of choosing wavelets based on the problem at hand is stressed. In Chapter 5, I introduce a wavelet design method that uses linear prediction in order to design wavelets that are geared to the signal or feature being analyzed. The use of these designed wavelets in a test feature identification application led to positive results. The methods developed in this thesis; the feature identification methods of ...
Date: June 1, 1997
Creator: Anant, K.S.
Partner: UNT Libraries Government Documents Department

Hanford Seismic Network

Description: This report describes the Hanford Seismic Network. The network consists of two instrument arrays: seismometers and strong motion accelerometers. The seismometers determine the location and magnitude of earthquakes, and the strong motion accelerometers determine ground motion. Together these instruments arrays comply with the intent of DOE Order 5480.20, Natural Phenomena Hazards Mitigation.
Date: May 1, 1997
Creator: Reidel, S.P. & Hartshorn, D.C.
Partner: UNT Libraries Government Documents Department

Comments on the geophysics paper -- Multiparameter l(1) norm waveform fitting: Interpretation of Gulf of Mexico reflection seismograms: by H. Djikpesse and A. Tarantola

Description: In their recent paper, Djikpesse and Tarantola (Geophysics 65 (4) pp. 1023-1035, hereinafter D and T) raise a central question about geophysical inversion: how accurately must the physics of seismic waves in the Earth be modeled in order that inversion succeed? Two general criteria for successful inversion appear in D and T's discussion: fit of predicted to observed data, and prediction of Earth structure. The hypothesis underlying inversion is that these criteria are unextricably linked, so that data fit should lead to accurate inference of subsurface features. The authors have also worked on the data discussed in D and T, using different modeling choices and inversion algorithms but also achieving quite successful inversions, in both senses. They feel that a brief comparison of methods and results might highlight the subtle relation between accuracy in modeling and success in inversion as well as raising questions about the appropriateness of D and T's modeling and inversion choices.
Date: January 3, 2000
Creator: Minkoff, S.E. & Symes, W.W.
Partner: UNT Libraries Government Documents Department

Preliminary noise survey and data report of Saudi Arabian data

Description: From November 1995 to March 1996 a total of 9 broadband temporary stations were deployed across Saudi Arabian shield. These stations consisted of STS-2 seismometers recorded continuously at 40 sps on RefTek dataloggers. All installations were at bedrock sites. Using data sections selected randomly during the deployment, noise studies showed that most stations were exceptionally quiet with noise level near the USGS low noise model for frequencies higher than 0.1 Hz. At lower frequencies, the horizontal components showed increased noise levels, possibly due to instrumental characteristics. High-frequency (greater than 1 Hz) noise varied as much as 10 db between day and night for some stations (RAYN, TAIF) while more isolated stations (HALM) were constant. Seasonal noise levels also varied, with April to June being the quietest months. Slight changes in peak microseism frequency also occurred seasonally.
Date: August 1, 1997
Creator: Mellors, R.
Partner: UNT Libraries Government Documents Department

Wave propagation modeling capabilities at LLNL: Applications to regional discrimination

Description: A primary goal of our research at LLNL has been to develop an assemblage of the most promising numerical techniques for simulating regional wave propagation through complex media. These numerical capabilities will be an integral part of our approach to regional characterization in both the Middle East and North Africa. In this paper, we focus on demonstrating and validating our current modeling capabilities, which include reflectivity, boundary integral, finite-difference, along with hybrid forms of these approaches. We use the boundary integral and finite-difference techniques to provide better understanding of regional discriminant variability along three arrays which were deployed to record regional signals from the NPE. These arrays extend west, northwest, and east from NTS, with the western line coinciding with one of three Southern Sierra Continental Dynamics (SSCD) refraction experiment profiles. This gives detailed coverage of regional phases along one of the most well constrained crustal profiles in the western United States. Phase amplitudes and the resulting discriminant variability are presented. This ``ground truth`` dataset will then act as the basis for the future validation of our numerical codes concurrent with our regionalization of the Middle East and North Africa.
Date: July 1, 1995
Creator: Schultz, C.A.; Larsen, S.C.; Goldstein, P. & Ruppert, S.D.
Partner: UNT Libraries Government Documents Department

Seismic activity associated with the September 1977 deflation of the Krafla central volcano in NE-Iceland

Description: The September 1977 deflation event in the Krafla caldera was one of a series of such events that has been in progress since December 1975. The operation of portable seismographs in the active region and favorable location of the main seismic activity with respect to the permanent seismograph network in NE-Iceland allow a more detailed study of this deflation event than most of the other events. Continuous volcanic tremor appeared on the local seismographs shortly before 16 h on September 8, 1977. Deflation of the volcano began at the same time. A small basaltic eruption broke out on a 0.9 km long fissure near the northern rim of the caldera at about 18 h. Earthquake activity increased soon after the beginning of the tremor and the first earthquakes were located in the caldera region. The earthquake activity then migrated southwards along the Krafla fault swarm with a speed of about 0.5 m sec{sup -1}, and culminated shortly before midnight with 8 earthquakes larger than magnitude 3 that were located near the Namafjall geothermal area 8 km south of the center of the caldera. Shortly after the earthquake activity migrated into the Namafjall area small amounts of basaltic pumice were erupted through a 1138 m deep drill hole there. Depths of earthquakes were 0-6 km in the northern part of the hypocentral zone and 0-4 in the southern part. The first motion pattern of P-waves suggests dip-slip faulting on steeply dipping fault planes consistent with the extensive normal faulting observed on the surface throughout the epicentral zone. The magnitude-frequency relationship was nonlinear and changed during the earthquake sequence. The seismological data strongly support the interpretation that deflation of the Krafla volcano is associated with horizontal migration of magma from the caldera region and formation of dykes in the Krafla fault swarm.
Date: January 1, 1979
Creator: Brandsdottir, Bryndis & Einarsson, Pall
Partner: UNT Libraries Government Documents Department

The effects of major structural features in Western China on explosion seismograms

Description: Synthetic explosion seismograms have been calculated on paths from Lop Nor to the NIL station in northern Pakistan, from NIL to Lop Nor, and from Lop Nor to the TLY station in the Baikal Rift. Computational studies were done of the influence on the character of the seismograms of major structural features such as sedimentary basins, topography associated with the Himalayas and the Tibetan Plateau, roughness of the Moho, and the presence of a deep Moho depression under the Tibetan Plateau, roughness of the Moho, and the presence of a deep Moho done with a 1-Hz Kelly waves source and 500-m resolution. Uniform elastic constants and frequency-independent quality factors, Q{sub p} and Q{sub s}, were used in each of three materials: basin sediments, crust, and mantle. The deep basins which due to the generation of large-amplitude Rayleigh waves at source-ward basin edges. In simulations done with the effects of anelastic attenuation included, the amplitude of passage across the 800-km-wide Tarim Basin on the Lop Nor -> NIL path but not on the 200-km path across the basin that straddles the Lop Nor -> TLY path.
Date: November 1, 1997
Creator: Jones, E.M.; App, F.N. & Bos, R.J.
Partner: UNT Libraries Government Documents Department

Synthetic seismograms at regional distances for May 1995 earthquake and explosion sources in Western China

Description: Waveforms recorded at several regional seismic stations at varying azimuths form explosion and earthquake sources in western China exhibit marked variation from station to station. We have performed two-dimensional finite difference simulations of these events, using moment tensor sources and simple crustal structure models, to generate synthetic seismograms at these locations. The synthetic seismograms at three locations exhibit behavior that is qualitatively consistent with the data, while computational results at a fourth station differ from the data. We discuss these results, the assumptions of the simulations, and the limitations of this type of modeling in the context of regional seismic propagation.
Date: August 1, 1996
Creator: App, F.N.; Bos, R.J. & Kamm, J.R.
Partner: UNT Libraries Government Documents Department

MatSeis: A Seismic toolbox for MATLAB

Description: To support the signal processing and data visualization needs of CTBT related projects at SNL, a MATLAB based GUI was developed. This program is known as MatSeis. MatSeis was developed quickly using the available MATLAB functionality. It provides a time-distance profile plot integrating origin, waveform, travel-time, and arrival data. Graphical plot controls, data manipulation, and signal processing functions provide a user friendly seismic analysis package. In addition, the full power of MATLAB (the premier tool for general numeric processing and visualization) is available for prototyping new functions by end users. This package is being made available to the seismic community in the hope that it will aid CTBT research and will facilitate cooperative signal processing development. 2 refs., 5 figs.
Date: August 1, 1996
Creator: Harris, J.M. & Young, C.J.
Partner: UNT Libraries Government Documents Department

Microearthquake Study of the Salton Sea Geothermal Field, California: Evidence of Stress Triggering - Masters Thesis

Description: A digital network of 24 seismograph stations was operated from September 15, 1987 to September 30, 1988, by Lawrence Livermore National Laboratory and Unocal as part of the Salton Sea Scientific Drilling Project to study seismicity related to tectonics and geothermal activity near the drilling site. More than 2001 microearthquakes were relocated in this study in order to image any pervasive structures that may exist within the Salton Sea geothermal field. First, detailed velocity models were obtained through standard 1-D inversion techniques. These velocity models were then used to relocate events using both single event methods and Double-Differencing, a joint hypocenter location method. An anisotropic velocity model was built from anisotropy estimates obtained from well logs within the study area. During the study period, the Superstition wills sequence occurred with two moderate earthquakes of MS 6.2 and MS 6.6. These moderate earthquakes caused a rotation of the stress field as observed from the inversion of first motion data from microearthquakes at the Salton Sea geothermal field. Coulomb failure analysis also indicates that microearthquakes occurring after the Superstition Hills sequence are located within a region of stress increase suggesting stress triggering caused by the moderate earthquakes.
Date: February 1, 2002
Creator: Holland, Austin Adams
Partner: UNT Libraries Government Documents Department

Cutting Costs by Locating High Production Wells: A Test of the Volcano seismic Approach to Finding ''Blind'' Resources

Description: In the summer of 2000, Duke University and the Kenyan power generation company, KenGen, conducted a microearthquake monitoring experiment at Longonot volcano in Kenya. Longonot is one of several major late Quaternary trachyte volcanoes in the Kenya Rift. They study was aimed at developing seismic methods for locating buried hydrothermal areas in the Rift on the basis of their microearthquake activity and wave propagation effects. A comparison of microearthquake records from 4.5 Hz, 2 Hz, and broadband seismometers revealed strong high-frequency site and wave-propagation effects. The lower frequency seismometers were needed to detect and record individual phases. Two-dozen 3-component 2- Hz L22 seismographs and PASSCAL loggers were then distributed around Longonot. Recordings from this network located one seismically active area on Longonot's southwest flank. The events from this area were emergent, shallow (<3 km), small (M<1), and spatially restricted. Evidently, the hydrothermal system in this area is not currently very extensive or active. To establish the nature of the site effects, the data were analyzed using three spectral techniques that reduce source effects. The data were also compared to a simple forward model. The results show that, in certain frequency ranges, the technique of dividing the horizontal motion by the vertical motion (H/V) to remove the source fails because of non-uniform vertical amplification. Outside these frequencies, the three methods resolve the same, dominant, harmonic frequencies at a given site. In a few cases, the spectra can be fit with forward models containing low velocity surface layers. The analysis suggests that the emergent, low frequency character of the microearthquake signals is due to attenuation and scattering in the near surface ash deposits.
Date: June 6, 2002
Creator: Shalev, Eylon; Malin, Peter E. & McCausland, Wendy
Partner: UNT Libraries Government Documents Department

The White Pine Mine explosively induced, controlled collapse experiment

Description: On September 3, 1995, the White Pine Mine, which is owned by Copper Range Company, conducted the first of a planned series of explosive removal of existing pillars in their underground mining operations. The purpose of this operation is to evaluate the effectiveness of pillar rubbilization and roof collapse for planned in-situ leaching of the copper ore from the rock mass. This type of seismic source is unique in that a large, delay fired, explosive source was expected to be followed by collapse of the rock immediately above the explosion into the void created. Characterization of this type of mining source is of interest to the Comprehensive Test Ban Treaty (CTBT) R&D Seismic Program due to its unique properties. These include the controlled nature of the source in time, location, and magnitude, the fact that the source is located in an active region of underground mining, and that natural collapse of large portions of this mine have occurred in the recent past. The Mine operator is concerned with the characterization of the vibration induced by both the explosive and implosive components of the procedure and determination of the depth to which chimneying of the roof proceeded. This report will document: The reasons for conducting both the explosively induced collapse and the Los Alamos National Laboratory CTBT R&D Experimental Field Program experiment; The local and regional seismic, acoustic, and videographic data acquired; Analysis of the explosion/collapse seismic signal generated; Analysis and location of the aftershocks associated with the collapse; and Conclusions made concerning this type of mining explosion in relation to verification of a Comprehensive Test Ban Treaty.
Date: September 1996
Creator: Pearson, D. C.; Stump, B. W. & Phillips, W. S.
Partner: UNT Libraries Government Documents Department

Source and Path Effects on Regional Phases in China

Description: As part of the CTBT Research and Development regional characterization effort, we are assembling, organizing and analyzing geological, geophysical,and seismic data for inclusion in a knowledge base for China. We have collected seismic data from 11 Chinese Digital Seismic Network (CDSN) stations as well as IRIS stations AAK, TLY, ULN and NIL from adjoining regions. Using the published event locations and origin times, we identify Pn, Pg, Sn, and Lg phases,construct travel time curves, and estimate apparent velocities from broadband and short period seismograms. Following this, we collect amplitudes of regional seismic phases and associated noise levels using bandpassed waveforms. Studies of path specific propagation of the seismic phases have mapped blockages and have generated corrections useful in reducing scatter in magnitude estimates and in discriminant ratios. Such path corrections reduce RMS distance and mb- corrected Lg amplitude to as much as 60% of its original level (log{sub 10} domain). Path corrections are less effective with Pn data. We also study source scaling effects on these data which will allow us to refine path corrections further.
Date: December 31, 1997
Creator: Phillips, W.S., Randall, G.E., Hartse, H.E., Taylor, S.R., Patton, H.J.
Partner: UNT Libraries Government Documents Department