Clark Dunson | Santa Clara University (original) (raw)

Papers by Clark Dunson

ABSTRACT We use long-term (1999-2004) ULF data (

Natural Hazards and Earth System Science, 2010

Analysis of the 2007 M5.4 Alum Rock earthquake near San José California showed that magnetic puls... more Analysis of the 2007 M5.4 Alum Rock earthquake near San José California showed that magnetic pulsations were present in large numbers and with significant amplitudes during the 2 week period leading up the event. These pulsations were 1-30 s in duration, had unusual polarities (many with only positive or only negative polarities versus both polarities), and were different than other pulsations observed over 2 years of data in that the pulse sequence was sustained over a 2 week period prior to the quake, and then disappeared shortly after the quake. A search for the underlying physics process that might explain these pulses was was undertaken, and one theory (Freund, 2002) demonstrated that charge carriers were released when various types of rocks were stressed in a laboratory environment. It was also significant that the observed charge carrier generation was transient, and resulted in pulsating current patterns. In an attempt to determine if this phenomenon occurred outside of the laboratory environment, the authors scaled up the physics experiment from a relatively small rock sample in a dry laboratory setting, to a large 7 metric tonne boulder comprised of Yosemite granite. This boulder was located in a natural, humid (above ground) setting at Bass Lake, Ca. The boulder was instrumented with two Zonge Engineering, Model ANT4 induction type magnetometers, two Trifield Air Ion Counters, a surface charge detector, a geophone, a Bruker Model EM27 Fourier Transform Infra Red (FTIR) spectrometer with Sterling cycle cooler, and various temperature sensors. The boulder was stressed over about 8 h using expanding concrete (Bustar tm), until it fractured into three major pieces. The recorded data showed surface charge build up, magnetic pulsations, impulsive air conductivity changes, and acoustical cues starting about 5 h before the boulder actually

Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress h... more Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress have been shown to emit a small but distinct excess amount of infrared (IR) light (Freund, F. T., et al, JASTP, 71, 2009). This anomalous IR emission arises from the radiative de-excitation of electron vacancy defects, which, upon stress-activation, flow into the unstressed portion and recombine at the surface. This non-thermal IR emission occurs in the 8 mum to 14 mum wavelength region. Field experiments are performed by slowly stressing large boulders and monitoring the IR emission in situ with a Bruker EM27 Fourier Transform Infrared (FTIR) spectrometer. The boulders are prepared by drilling four blind holes into the rock, 50-100 cm deep, in an array roughly parallel to, and behind, the surface from where the IR emission is monitored. Any debris and water is blown out of the boreholes with compressed air, and the rock is given time to dry and relax from drilling-induced stresses. The h...

Annales Geophysicae, 2008

We examine the association between earthquakes and Pc1 pulsations observed at a low-latitude stat... more We examine the association between earthquakes and Pc1 pulsations observed at a low-latitude station in Parkfield, California. The period under examination is ∼7.5 years in total, from February 1999 to July 2006, and we use an automatic identification algorithm to extract information on Pc1 pulsations from the magnetometer data. These pulsations are then statistically correlated to earthquakes from the USGS NEIC catalog within a radius of 200 km around the magnetometer, and M>3.0. Results indicate that there is an enhanced occurrence probability of Pc1 pulsations ∼5-15 days in advance of the earthquakes, during the daytime. We quantify the statistical significance and show that such an enhancement is unlikely to have occurred due to chance alone. We then examine the effect of declustering our earthquake catalog, and show that even though significance decreases, there is still a statistically significant daytime enhancement prior to the earthquakes. Finally, we select only daytime Pc1 pulsations as the fiducial time of our analysis, and show that earthquakes are ∼3-5 times more likely to occur in the week following these pulsations, than normal. Comparing these results to other events, it is preliminarily shown that the normal earthquake probability is unaffected by geomagnetic activity, or a random event sequence.

Annales Geophysicae, 2010

We use a relatively simple model of an underground current source co-located with the earthquake ... more We use a relatively simple model of an underground current source co-located with the earthquake hypocenter to estimate the magnitude of the seismotelluric current required to produce observable ground signatures. The Alum Rock earthquake of 31 October 2007, is used as an archetype of a typical California earthquake, and the effects of varying the ground conductivity and length of the current element are examined. Results show that for an observed 30 nT pulse at 1 Hz, the expected seismotelluric current magnitudes fall in the range ∼10-100 kA. By setting the detectability threshold to 1 pT, we show that even when large values of ground conductivity are assumed, magnetic signals are readily detectable within a range of 30 km from the epicenter. When typical values of ground conductivity are assumed, the minimum current required to produce an observable signal within a 30 km range was found to be ∼1 kA, which is a surprisingly low value. Furthermore, we show that deep nulls in the signal power develop in the non-cardinal directions relative to the orientation of the source current, indicating that a magnetometer station located in those regions may not observe a signal even though it is well within the detectable range. This result underscores the importance of using a network of magnetometers when searching for preseismic electromagnetic signals.

ArXiv, 2021

The muzzle blast caused by the discharge of a firearm generates a loud, impulsive sound that prop... more The muzzle blast caused by the discharge of a firearm generates a loud, impulsive sound that propagates away from the shooter in all directions. The location of the source can be computed from time-of-arrival measurements of the muzzle blast on multiple acoustic sensors at known locations, a technique known as multilateration. The multilateration problem is considerably simplified by assuming straight-line propagation in a homogeneous medium, a model for which there are multiple published solutions. Live-fire tests of the ShotSpotter gunshot location system in Pittsburgh, PA were analyzed off-line under several algorithms and geometric constraints to evaluate the accuracy of acoustic multilateration in a forensic context. Best results were obtained using the algorithm due to Mathias, Leonari and Galati under a two-dimensional geometric constraint. Multilateration on random subsets of the participating sensor array show that 96% of shots can be located to an accuracy of 15 m or bette...

Earth, Planets and Space

When working with ultra-low-frequency (ULF) magnetic datasets, as with most geophysical time-seri... more When working with ultra-low-frequency (ULF) magnetic datasets, as with most geophysical time-series data, it is important to be able to distinguish between cultural signals, internal instrument noise, and natural external signals with their induced telluric fields. This distinction is commonly attempted using simultaneously recorded data from a spatially remote reference site. Here, instead, we compared data recorded by two systems with different instrumental characteristics at the same location over the same time period. We collocated two independent ULF magnetic systems, one from the QuakeFinder network and the other from the United States Geological Survey (USGS)-Stanford network, in order to cross-compare their data, characterize data reproducibility, and characterize signal origin. In addition, we used simultaneous measurements at a remote geomagnetic observatory to distinguish global atmospheric signals from local cultural signals. We demonstrated that the QuakeFinder and USGS-Stanford systems have excellent coherence, despite their different sensors and digitizers. Rare instances of isolated signals recorded by only one system or only one sensor indicate that caution is needed when attributing specific recorded signal features to specific origins.

DESCRIPTION Stress-dependent voltage offsets from polymer insulators used in rock mechanics and m... more DESCRIPTION Stress-dependent voltage offsets from polymer insulators used in rock mechanics and material testing

This paper addresses a case study of the Dec. 22 2004, M6.4 San Simeon earthquake in California, ... more This paper addresses a case study of the Dec. 22 2004, M6.4 San Simeon earthquake in California, and compares both space and ground ELF signatures. Preliminary results of the satellite collections showed unique signals prior to and after the San Simeon quake, as well as several other large world-wide quakes. Ground collections were inconclusive since the closest 4 sensors of the available 35 sensors were located more than 60 km and 2 parallel fault traces away from the San Simeon quake epicenter.

There have been a number of reports of interesting electromagnetic (EM) signals detected prior to... more There have been a number of reports of interesting electromagnetic (EM) signals detected prior to large earthquakes, but the subsequent analyses have been hampered by insufficient instrumentation to cover large geographical areas, and enough data history to allow statistical analyses of potential "earthquake signatures". The EM data analysis requires that several basic questions be addressed: "What are the "normal" background signatures (both natural and man-made) for each instrument during non-earthquake days?" and "What are the statistically "unique" signatures associated with large earthquakes?" Both ground and space sensors are subjected to a wide variety of non-earthquake EM noise (geomagnetic micropulsations, SRS, Schumann Resonance and man-made EM noise). We first show the top-level strategy developed by QuakeFinder and our partners to collect large volumes of satellite EM data (DEMETER and QuakeSat), and ground EM data (from ...

A collaboration between QuakeFinder (Palo Alto) and NASA JPL utilized both ground and space instr... more A collaboration between QuakeFinder (Palo Alto) and NASA JPL utilized both ground and space instruments to observe a series of electromagnetic (EM) signals detected up to 2 weeks prior to the Oct 30, 2007 Alum Rock, California, M5.4 earthquake. These signals included Ultra Low Frequency (ULF: 0.01 to 12 Hz) pulsations that were detected with a 3 axis induction magnetometer located 2 km from the epicenter. The 1- 12 sec wide pulsations were 10-50 times more intense than 2 year normal background noise levels, and the pulsations occurred 10-30 times more frequently in the 2 weeks prior to the quake than the average pulse count for the 1.8 years prior. The air conductivity sensor at the same site saturated for much of the evening prior to the quake. The conductivity levels were compared to the previous year's average conductivity patterns at the site, and determined not to be caused by moisture contamination. The GOES-West weather satellite typically observes the west coast of Calif...

The common characteristics of the signal found in the 0.0025-0.025 Hz portion of the geomagnetic ... more The common characteristics of the signal found in the 0.0025-0.025 Hz portion of the geomagnetic spectrum are presented as measured by the CalMagNet high-resolution search coil network. Coherence, azimuth ratio, and timing of wave characteristics are depicted, showing their statistical variances, and potential for revealing residual local signals. The low coherence frequency band near 0.1Hz is compared with higher coherence signals at lower frequencies. Also presented are the results of comparing the characteristics of these signals around the time of earthquakes near the sensors as compared to control periods of data during non-earthquake periods.

Magnetic signal fluctuations that are potentially related to earthquake occurrences have been rep... more Magnetic signal fluctuations that are potentially related to earthquake occurrences have been reported for a number of years. Recently, short-duration pulses have been shown to occur in association with the Tacna, Peru M6.2 earthquake (May 6, 2010 02:42:47 UTC 18.02°S 70.53°W) and the Alum Rock M5.4 quake (Oct 31,03:04 UTC 2007 Lat 37.43N Long 121.78W), but since these are only 2 events, it is not clear how statistically significant these results are. Here, we use a novel algorithm to process several years of magnetometer data and automatically extract and classify any pulses that may have occurred. The list of pulses is then sorted according to clustering of parameters, typical noise sources are identified and removed, and the relation of the remaining pulses to earthquakes is examined on a statistical basis.

The DEMETER satellite, designed with the objective of investigating ionospheric phenomena before ... more The DEMETER satellite, designed with the objective of investigating ionospheric phenomena before earthquakes, measures the in-situ electron density at ~700 km height using a Langemuir probe. On the other hand, dual-frequency GPS data can be used to retrieve the Integrated Electron Content (IEC) along the ray path from ground stations to GPS satellites. We compare electron density data acquired by

ABSTRACT Using the triaxial search-coil magnetometer data in the ~ 1 Hz to 18 kHz frequency range... more ABSTRACT Using the triaxial search-coil magnetometer data in the ~ 1 Hz to 18 kHz frequency range from the low altitude (~710 km), high-inclination (~ 82°), DEMETER satellite, we perform a statistical search for magnetic signals that precede, coincide with, and succeed large earthquakes. We identify DEMETER passes that have occurred in a spatial region of radius ~ 3000 km around the epicenter, and -30 to +10 days around the time of large (M > 5) earthquakes, and perform a superposed epoch analysis of the signal amplitude in various frequency bands as a function of distance and time. This technique is useful in revealing weak signals that are associated in a systematic way with a given event, in our case seismic activity. We then subdivide the superposed epoch analysis plane into a "near" (0-1000 km) and "far" (2000-3000 km) regions relative to each earthquake, and compute the ratio R=near/far signals to test for any proximity effects. Finally, we subdivide all our data into a number of time periods, and perform the above analysis in each period, finally checking for repeatability amongst each of the separate periods. The above analysis is repeated under a variety of conditions, for example, only testing for shallow earthquakes, dividing the earthquakes into 3 types (normal/reverse/strike-slip), or only considering intense (M>6, 6.5, etc.) earthquakes. We present the results of our analysis with an extensive discussion of our methods.

ABSTRACT Pulsations are known to occur in the 0.005 - 0.1 Hz (period = 10 sec-150 sec) portion of... more ABSTRACT Pulsations are known to occur in the 0.005 - 0.1 Hz (period = 10 sec-150 sec) portion of the geomagnetic spectrum as a strong signal. They have been designated as Pc 3 &4, and prior work has sought to determine the structure of the magnetospheric standing waves for use in estimating density of the plasmasphere, etc. (Russell, et al. [1998]). Pc 3-4 characteristics also have held long interest for seismologists, as they are a form of interference when using digital seismometers to attempt measurements of long-period motion. Another recent source of interest in these pulsations stems from the announcement that some researchers have seen fluctuations in the geomagnetic signal associated with earthquakes. Reports of these anomalies have spanned frequencies in the range of 0.01 Hz, thus long term monitoring of Pc3-4 activity over California may be critical in defining the normal, background signal levels when looking for potential earthquake-related ULF signals. The deployment of high-resolution search coils in Quakefinder's CalMagNet in 2005, have allowed a much higher resolution and wider geographic distribution of measurements to study these complex signals. The analytical techniques of multi- channel coherence, wave analysis, and signal space separation provide unique characterizations of these signals, including latitude dependency. Progress in studying the geomagnetic signal using these techniques is presented, the signal estimator's design is shown, and future directions are discussed.

Since ultra-low frequency (ULF) magnetic anomalies were discovered prior to the 1989 Loma Prieta,... more Since ultra-low frequency (ULF) magnetic anomalies were discovered prior to the 1989 Loma Prieta, Ca. M7.0 earthquake, QuakeFinder, a small R&D group based in Palo Alto California has systematically monitored ULF magnetic signals with a network of 3-axis induction magnetometers since 2000 in California. This raw magnetometer data was collected at 20-50 samples per sec., with no preprocessing, in an

ABSTRACT We use long-term (1999-2004) ULF data (

Natural Hazards and Earth System Science, 2010

Analysis of the 2007 M5.4 Alum Rock earthquake near San José California showed that magnetic puls... more Analysis of the 2007 M5.4 Alum Rock earthquake near San José California showed that magnetic pulsations were present in large numbers and with significant amplitudes during the 2 week period leading up the event. These pulsations were 1-30 s in duration, had unusual polarities (many with only positive or only negative polarities versus both polarities), and were different than other pulsations observed over 2 years of data in that the pulse sequence was sustained over a 2 week period prior to the quake, and then disappeared shortly after the quake. A search for the underlying physics process that might explain these pulses was was undertaken, and one theory (Freund, 2002) demonstrated that charge carriers were released when various types of rocks were stressed in a laboratory environment. It was also significant that the observed charge carrier generation was transient, and resulted in pulsating current patterns. In an attempt to determine if this phenomenon occurred outside of the laboratory environment, the authors scaled up the physics experiment from a relatively small rock sample in a dry laboratory setting, to a large 7 metric tonne boulder comprised of Yosemite granite. This boulder was located in a natural, humid (above ground) setting at Bass Lake, Ca. The boulder was instrumented with two Zonge Engineering, Model ANT4 induction type magnetometers, two Trifield Air Ion Counters, a surface charge detector, a geophone, a Bruker Model EM27 Fourier Transform Infra Red (FTIR) spectrometer with Sterling cycle cooler, and various temperature sensors. The boulder was stressed over about 8 h using expanding concrete (Bustar tm), until it fractured into three major pieces. The recorded data showed surface charge build up, magnetic pulsations, impulsive air conductivity changes, and acoustical cues starting about 5 h before the boulder actually

Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress h... more Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress have been shown to emit a small but distinct excess amount of infrared (IR) light (Freund, F. T., et al, JASTP, 71, 2009). This anomalous IR emission arises from the radiative de-excitation of electron vacancy defects, which, upon stress-activation, flow into the unstressed portion and recombine at the surface. This non-thermal IR emission occurs in the 8 mum to 14 mum wavelength region. Field experiments are performed by slowly stressing large boulders and monitoring the IR emission in situ with a Bruker EM27 Fourier Transform Infrared (FTIR) spectrometer. The boulders are prepared by drilling four blind holes into the rock, 50-100 cm deep, in an array roughly parallel to, and behind, the surface from where the IR emission is monitored. Any debris and water is blown out of the boreholes with compressed air, and the rock is given time to dry and relax from drilling-induced stresses. The h...

Annales Geophysicae, 2008

We examine the association between earthquakes and Pc1 pulsations observed at a low-latitude stat... more We examine the association between earthquakes and Pc1 pulsations observed at a low-latitude station in Parkfield, California. The period under examination is ∼7.5 years in total, from February 1999 to July 2006, and we use an automatic identification algorithm to extract information on Pc1 pulsations from the magnetometer data. These pulsations are then statistically correlated to earthquakes from the USGS NEIC catalog within a radius of 200 km around the magnetometer, and M>3.0. Results indicate that there is an enhanced occurrence probability of Pc1 pulsations ∼5-15 days in advance of the earthquakes, during the daytime. We quantify the statistical significance and show that such an enhancement is unlikely to have occurred due to chance alone. We then examine the effect of declustering our earthquake catalog, and show that even though significance decreases, there is still a statistically significant daytime enhancement prior to the earthquakes. Finally, we select only daytime Pc1 pulsations as the fiducial time of our analysis, and show that earthquakes are ∼3-5 times more likely to occur in the week following these pulsations, than normal. Comparing these results to other events, it is preliminarily shown that the normal earthquake probability is unaffected by geomagnetic activity, or a random event sequence.

Annales Geophysicae, 2010

We use a relatively simple model of an underground current source co-located with the earthquake ... more We use a relatively simple model of an underground current source co-located with the earthquake hypocenter to estimate the magnitude of the seismotelluric current required to produce observable ground signatures. The Alum Rock earthquake of 31 October 2007, is used as an archetype of a typical California earthquake, and the effects of varying the ground conductivity and length of the current element are examined. Results show that for an observed 30 nT pulse at 1 Hz, the expected seismotelluric current magnitudes fall in the range ∼10-100 kA. By setting the detectability threshold to 1 pT, we show that even when large values of ground conductivity are assumed, magnetic signals are readily detectable within a range of 30 km from the epicenter. When typical values of ground conductivity are assumed, the minimum current required to produce an observable signal within a 30 km range was found to be ∼1 kA, which is a surprisingly low value. Furthermore, we show that deep nulls in the signal power develop in the non-cardinal directions relative to the orientation of the source current, indicating that a magnetometer station located in those regions may not observe a signal even though it is well within the detectable range. This result underscores the importance of using a network of magnetometers when searching for preseismic electromagnetic signals.

ArXiv, 2021

The muzzle blast caused by the discharge of a firearm generates a loud, impulsive sound that prop... more The muzzle blast caused by the discharge of a firearm generates a loud, impulsive sound that propagates away from the shooter in all directions. The location of the source can be computed from time-of-arrival measurements of the muzzle blast on multiple acoustic sensors at known locations, a technique known as multilateration. The multilateration problem is considerably simplified by assuming straight-line propagation in a homogeneous medium, a model for which there are multiple published solutions. Live-fire tests of the ShotSpotter gunshot location system in Pittsburgh, PA were analyzed off-line under several algorithms and geometric constraints to evaluate the accuracy of acoustic multilateration in a forensic context. Best results were obtained using the algorithm due to Mathias, Leonari and Galati under a two-dimensional geometric constraint. Multilateration on random subsets of the participating sensor array show that 96% of shots can be located to an accuracy of 15 m or bette...

Earth, Planets and Space

When working with ultra-low-frequency (ULF) magnetic datasets, as with most geophysical time-seri... more When working with ultra-low-frequency (ULF) magnetic datasets, as with most geophysical time-series data, it is important to be able to distinguish between cultural signals, internal instrument noise, and natural external signals with their induced telluric fields. This distinction is commonly attempted using simultaneously recorded data from a spatially remote reference site. Here, instead, we compared data recorded by two systems with different instrumental characteristics at the same location over the same time period. We collocated two independent ULF magnetic systems, one from the QuakeFinder network and the other from the United States Geological Survey (USGS)-Stanford network, in order to cross-compare their data, characterize data reproducibility, and characterize signal origin. In addition, we used simultaneous measurements at a remote geomagnetic observatory to distinguish global atmospheric signals from local cultural signals. We demonstrated that the QuakeFinder and USGS-Stanford systems have excellent coherence, despite their different sensors and digitizers. Rare instances of isolated signals recorded by only one system or only one sensor indicate that caution is needed when attributing specific recorded signal features to specific origins.

DESCRIPTION Stress-dependent voltage offsets from polymer insulators used in rock mechanics and m... more DESCRIPTION Stress-dependent voltage offsets from polymer insulators used in rock mechanics and material testing

This paper addresses a case study of the Dec. 22 2004, M6.4 San Simeon earthquake in California, ... more This paper addresses a case study of the Dec. 22 2004, M6.4 San Simeon earthquake in California, and compares both space and ground ELF signatures. Preliminary results of the satellite collections showed unique signals prior to and after the San Simeon quake, as well as several other large world-wide quakes. Ground collections were inconclusive since the closest 4 sensors of the available 35 sensors were located more than 60 km and 2 parallel fault traces away from the San Simeon quake epicenter.

There have been a number of reports of interesting electromagnetic (EM) signals detected prior to... more There have been a number of reports of interesting electromagnetic (EM) signals detected prior to large earthquakes, but the subsequent analyses have been hampered by insufficient instrumentation to cover large geographical areas, and enough data history to allow statistical analyses of potential "earthquake signatures". The EM data analysis requires that several basic questions be addressed: "What are the "normal" background signatures (both natural and man-made) for each instrument during non-earthquake days?" and "What are the statistically "unique" signatures associated with large earthquakes?" Both ground and space sensors are subjected to a wide variety of non-earthquake EM noise (geomagnetic micropulsations, SRS, Schumann Resonance and man-made EM noise). We first show the top-level strategy developed by QuakeFinder and our partners to collect large volumes of satellite EM data (DEMETER and QuakeSat), and ground EM data (from ...

A collaboration between QuakeFinder (Palo Alto) and NASA JPL utilized both ground and space instr... more A collaboration between QuakeFinder (Palo Alto) and NASA JPL utilized both ground and space instruments to observe a series of electromagnetic (EM) signals detected up to 2 weeks prior to the Oct 30, 2007 Alum Rock, California, M5.4 earthquake. These signals included Ultra Low Frequency (ULF: 0.01 to 12 Hz) pulsations that were detected with a 3 axis induction magnetometer located 2 km from the epicenter. The 1- 12 sec wide pulsations were 10-50 times more intense than 2 year normal background noise levels, and the pulsations occurred 10-30 times more frequently in the 2 weeks prior to the quake than the average pulse count for the 1.8 years prior. The air conductivity sensor at the same site saturated for much of the evening prior to the quake. The conductivity levels were compared to the previous year's average conductivity patterns at the site, and determined not to be caused by moisture contamination. The GOES-West weather satellite typically observes the west coast of Calif...

The common characteristics of the signal found in the 0.0025-0.025 Hz portion of the geomagnetic ... more The common characteristics of the signal found in the 0.0025-0.025 Hz portion of the geomagnetic spectrum are presented as measured by the CalMagNet high-resolution search coil network. Coherence, azimuth ratio, and timing of wave characteristics are depicted, showing their statistical variances, and potential for revealing residual local signals. The low coherence frequency band near 0.1Hz is compared with higher coherence signals at lower frequencies. Also presented are the results of comparing the characteristics of these signals around the time of earthquakes near the sensors as compared to control periods of data during non-earthquake periods.

Magnetic signal fluctuations that are potentially related to earthquake occurrences have been rep... more Magnetic signal fluctuations that are potentially related to earthquake occurrences have been reported for a number of years. Recently, short-duration pulses have been shown to occur in association with the Tacna, Peru M6.2 earthquake (May 6, 2010 02:42:47 UTC 18.02°S 70.53°W) and the Alum Rock M5.4 quake (Oct 31,03:04 UTC 2007 Lat 37.43N Long 121.78W), but since these are only 2 events, it is not clear how statistically significant these results are. Here, we use a novel algorithm to process several years of magnetometer data and automatically extract and classify any pulses that may have occurred. The list of pulses is then sorted according to clustering of parameters, typical noise sources are identified and removed, and the relation of the remaining pulses to earthquakes is examined on a statistical basis.

The DEMETER satellite, designed with the objective of investigating ionospheric phenomena before ... more The DEMETER satellite, designed with the objective of investigating ionospheric phenomena before earthquakes, measures the in-situ electron density at ~700 km height using a Langemuir probe. On the other hand, dual-frequency GPS data can be used to retrieve the Integrated Electron Content (IEC) along the ray path from ground stations to GPS satellites. We compare electron density data acquired by

ABSTRACT Using the triaxial search-coil magnetometer data in the ~ 1 Hz to 18 kHz frequency range... more ABSTRACT Using the triaxial search-coil magnetometer data in the ~ 1 Hz to 18 kHz frequency range from the low altitude (~710 km), high-inclination (~ 82°), DEMETER satellite, we perform a statistical search for magnetic signals that precede, coincide with, and succeed large earthquakes. We identify DEMETER passes that have occurred in a spatial region of radius ~ 3000 km around the epicenter, and -30 to +10 days around the time of large (M > 5) earthquakes, and perform a superposed epoch analysis of the signal amplitude in various frequency bands as a function of distance and time. This technique is useful in revealing weak signals that are associated in a systematic way with a given event, in our case seismic activity. We then subdivide the superposed epoch analysis plane into a "near" (0-1000 km) and "far" (2000-3000 km) regions relative to each earthquake, and compute the ratio R=near/far signals to test for any proximity effects. Finally, we subdivide all our data into a number of time periods, and perform the above analysis in each period, finally checking for repeatability amongst each of the separate periods. The above analysis is repeated under a variety of conditions, for example, only testing for shallow earthquakes, dividing the earthquakes into 3 types (normal/reverse/strike-slip), or only considering intense (M>6, 6.5, etc.) earthquakes. We present the results of our analysis with an extensive discussion of our methods.

ABSTRACT Pulsations are known to occur in the 0.005 - 0.1 Hz (period = 10 sec-150 sec) portion of... more ABSTRACT Pulsations are known to occur in the 0.005 - 0.1 Hz (period = 10 sec-150 sec) portion of the geomagnetic spectrum as a strong signal. They have been designated as Pc 3 &4, and prior work has sought to determine the structure of the magnetospheric standing waves for use in estimating density of the plasmasphere, etc. (Russell, et al. [1998]). Pc 3-4 characteristics also have held long interest for seismologists, as they are a form of interference when using digital seismometers to attempt measurements of long-period motion. Another recent source of interest in these pulsations stems from the announcement that some researchers have seen fluctuations in the geomagnetic signal associated with earthquakes. Reports of these anomalies have spanned frequencies in the range of 0.01 Hz, thus long term monitoring of Pc3-4 activity over California may be critical in defining the normal, background signal levels when looking for potential earthquake-related ULF signals. The deployment of high-resolution search coils in Quakefinder's CalMagNet in 2005, have allowed a much higher resolution and wider geographic distribution of measurements to study these complex signals. The analytical techniques of multi- channel coherence, wave analysis, and signal space separation provide unique characterizations of these signals, including latitude dependency. Progress in studying the geomagnetic signal using these techniques is presented, the signal estimator's design is shown, and future directions are discussed.

Since ultra-low frequency (ULF) magnetic anomalies were discovered prior to the 1989 Loma Prieta,... more Since ultra-low frequency (ULF) magnetic anomalies were discovered prior to the 1989 Loma Prieta, Ca. M7.0 earthquake, QuakeFinder, a small R&D group based in Palo Alto California has systematically monitored ULF magnetic signals with a network of 3-axis induction magnetometers since 2000 in California. This raw magnetometer data was collected at 20-50 samples per sec., with no preprocessing, in an