scholarly journals Seismic imaging of the shallow subsurface with high frequency seismic measurements

1998 ◽  
Author(s):  
Bruno Kaelin
Keyword(s):  
High Frequency ◽  
Seismic Imaging ◽  
Shallow Subsurface ◽  
Seismic Measurements

A Subsurface Geologic Feature Inferred from Relocation of Local Earthquakes in Al-Refaei District, Southern Iraq

2020 ◽  
Vol 54 (1A) ◽  
pp. 35-43
Author(s):  
Ali Ramthan
Keyword(s):  
High Frequency ◽  
Tectonic Setting ◽  
Arabian Plate ◽  
Stress Regime ◽  
Shallow Subsurface ◽  
Linear Feature ◽  
Recording Station ◽  
Communications System ◽  
System Power ◽  
Southern Iraq

For the last two decades, the District of Al-Refaei, southern Iraq, experienced several small to moderate size earthquakes that seem to be clustered in a relatively small area. The initial locations of these earthquakes from the available local and international bulletins show scattered events without any clear structural patterns. A seven-elements seismic array was installed for the period 2014 to 2018 to monitor this activity. Each element of the array consists of three-component Geospace GS11d high-frequency (4.5 Hz) geophone, a solar system power source, and telemetry communications system to transmit data to a central recording station. During the period of monitoring, the array recorded more than 56 earthquakes having a range of magnitude between 1.5 ML to 4.7 mb. Large number of the low magnitude earthquakes were not detected by other monitoring agencies; however, they were recorded by the array. Fifty-six of the most clearly recorded earthquakes were screened for relocation and analysis. Out of the 56 screened earthquakes, 35 were detected by the array alone. The majority of the selected earthquakes having their initial locations within the array. This improves the relocation process and increase accuracy. The relocated earthquakes express a clear pattern of a linear feature which strikes in the northwest-southeast direction. The direction of the newly inferred pattern coincides with the general tectonic setting of Iraq as it is parallel to Zagros suture zone and the general stress regime of the Arabian Plate. The depth of the relocated earthquakes ranges from about 3.9km to 8.9km. This indicates that these earthquakes occur along a shallow subsurface fault that was not mapped before.

Effects of magnetite on high-frequency ground-penetrating radar

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. H1-H11 ◽  
Author(s):  
Remke L. Van Dam ◽  
Jan M. H. Hendrickx ◽  
Nigel J. Cassidy ◽  
Ryan E. North ◽  
Mine Dogan ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
High Frequency ◽  
Laboratory Experiments ◽  
Parent Material ◽  
Electromagnetic Properties ◽  
Small Scale ◽  
Shallow Subsurface ◽  
Propagation Behavior ◽  
Ground Penetrating ◽  
Reflection Characteristics

Large concentrations of magnetite in sedimentary deposits and soils with igneous parent material have been reported to affect geophysical sensor performance. We have undertaken the first systematic experimental effort to understand the effects of magnetite for ground-penetrating radar (GPR) characterization of the shallow subsurface. Laboratory experiments were conducted to study how homogeneous magnetite-sand mixtures and magnetite concentrated in layers affect the propagation behavior (velocity, attenuation) of high-frequency GPR waves and the reflection characteristics of a buried target. Important observations were that magnetite had a strong effect on signal velocity and reflection, at magnitudes comparable to what has been observed in small-scale laboratory experiments that measured electromagnetic properties of magnetite-silica mixtures. Magnetite also altered signal attenuation and affected the reflection characteristics of buried targets. Our results indicated important implications for several fields, including land mine detection, Martian exploration, engineering, and moisture mapping using satellite remote sensing and radiometers.

scholarly journals Detecting Buried Human Bodies Using Ground-Penetrating Radar

2016 ◽  
Vol 5 (2) ◽  
pp. 59 ◽  
Author(s):  
Widodo Widodo ◽  
Iqbal F. Aditama ◽  
Khalid Syaifullah ◽  
Muthi’a J. Mahya ◽  
M. Hidayat
Keyword(s):  
Ground Penetrating Radar ◽  
High Frequency ◽  
Geophysical Methods ◽  
Tectonic Activity ◽  
Forensic Evidence ◽  
Shallow Subsurface ◽  
Disaster Victims ◽  
The Earth ◽  
Effectiveness And Efficiency ◽  
Ground Penetrating

Being located at the dense tectonic activity area, Indonesia has to cope with the constant risk of earthquakes. High frequency of earthquakes occurrence causes the crust instability and leads into another natural disaster such as landslides. Sometimes, the landslide avalanches are covering the high populated area destroying buildings and causing victims. Unfortunately, the treatment for the affected building and landslide victims searching are still using conventional methods. The purpose of this study is to detect buried human bodies using GPR method, so it can increase the effectiveness and the efficiency of disaster victims searching under the landslide avalanche. Ground-penetrating radar (GPR) is one of the geophysical methods that can be used to study shallow subsurface of the earth. GPR has been successfully used to locate grave and forensic evidence. However, more controlled research is needed to improve the effectiveness and efficiency of disaster victim detection that buried under landslides or earthquake avalanche. A detailed GPR survey was conducted in the Cikutra graveyard, Bandung, with corpses buried one week until two months before the survey. The radar profiles from this survey showed the clear amplitude contrast anomalies, emanated from the corpses. The strongest amplitude contrasts are observed at most recent grave compared to the older grave. We obtained the amplitude contrast at around 1.2 meters depth which is consistent with the depth of the buried corpses. In addition, the results of forward modeling of homogenous subsurface and corpses in subsurface will be presented.

scholarly journals Understanding Seismic Waves Generated by Train Traffic via Modeling: Implications for Seismic Imaging and Monitoring

2020 ◽  
Vol 92 (1) ◽  
pp. 287-300
Author(s):  
François Lavoué ◽  
Olivier Coutant ◽  
Pierre Boué ◽  
Laura Pinzon-Rincon ◽  
Florent Brenguier ◽  
...  
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Seismic Imaging ◽  
Moving Load ◽  
Frequency Content ◽  
Important Conclusion ◽  
Near Surface ◽  
Radiated Energy ◽  
Train Speed ◽  
High Frequency Content

Abstract Trains are now recognized as powerful sources for seismic interferometry based on noise correlation, but the optimal use of these signals still requires a better understanding of their source mechanisms. Here, we present a simple approach for modeling train-generated signals inspired by early work in the engineering community, assuming that seismic waves are emitted by sleepers regularly spaced along the railway and excited by passing train wheels. Our modeling reproduces well seismological observations of tremor-like emergent signals and of their harmonic spectra. We illustrate how these spectra are modulated by wheel spacing, and how their high-frequency content is controlled by the distribution of axle loads over the rail, which mainly depends on ground stiffness beneath the railway. This is summarized as a simple rule of thumb that predicts the frequency bands in which most of train-radiated energy is expected, as a function of train speed and of axle distance within bogies. Furthermore, we identify two end-member mechanisms—single stationary source versus single moving load—that explain two types of documented observations, characterized by different spectral signatures related to train speed and either wagon length or sleeper spacing. In view of using train-generated signals for seismic applications, an important conclusion is that the frequency content of the signals is dominated by high-frequency harmonics and not by fundamental modes of vibrations. Consequently, most train traffic worldwide is expected to generate signals with a significant high-frequency content, in particular in the case of trains traveling at variable speeds that produce truly broadband signals. Proposing a framework for predicting train-generated seismic wavefields over meters to kilometers distance from railways, this work paves the way for high-resolution passive seismic imaging and monitoring at different scales with applications to near-surface surveys (aquifers, civil engineering), natural resources exploration, and natural hazard studies (landslides, earthquakes, and volcanoes).

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