FIRST RESULTS FROM ELECTRICAL AND SEISMIC STUDIES OF LOW‐RESISTIVITY, LOW‐VELOCITY MATERIAL BENEATH EASTERN COLORADO

Geophysics ◽  
1977 ◽  
Vol 42 (4) ◽  
pp. 804-810 ◽  
Author(s):  
M. Landisman ◽  
W. Chaipayungpun
Keyword(s):  
Seismic Refraction ◽  
Impedance Tensor ◽  
High Plains ◽  
Low Velocity ◽  
Low Resistivity ◽  
Field Recordings ◽  
Pierre Shale ◽  
West Texas ◽  
First Results ◽  
Local Water

First results are reported for magnetotelluric (MT) observed apparent resistivities and phases, corresponding to both off‐diagonal components of the 2 by 2 electromagnetic impedance tensor, derived from E and H field recordings near Anton, in the High Plains of eastern Colorado. The data were recorded by a gain ranged, multichannel, multirate digital field system. The results, which span a frequency range of roughly [Formula: see text], extend from about 0.05 sec (20 Hz) to several thousand seconds. Corresponding sets of tightly clustered, practically continuous MT apparent resistivities and phases are virtually identical, constituting strong evidence for lateral homogeneity and isotropy of the electrical conductivity near this site. The derived one‐dimensional resistivity‐depth model is concordant with the depth and thickness of the local water table, with resistivities and depths for the Pierre shale derived from nearby well logs, with reconnaissance audiomagnetotelluric (AMT) data, and with ultra‐long period apparent resistivities derived from regional Deep Geomagnetic Sounding observations. The derived resistivity depth distribution also compares well with the depth to the crystalline basement from the neighboring U.S.G.S. Lamar‐Sterling, Colorado, seismic refraction profile. The concordance, between depths interpreted for a mid‐crustal seismic low‐velocity zone and a corresponding low‐resistivity zone at this site, parallels similar results previously reported for west Texas‐eastern New Mexico, and various sites in the U.S.S.R.

ELECTRICAL AND SEISMIC PROPERTIES OF THE EARTH’S CRUST IN THE SOUTHWESTERN GREAT PLAINS OF THE U.S.A.

Geophysics ◽  
1971 ◽  
Vol 36 (2) ◽  
pp. 363-381 ◽  
Author(s):  
B. J. Mitchell ◽  
M. Landisman
Keyword(s):  
Great Plains ◽  
Seismic Velocity ◽  
Impedance Tensor ◽  
Seismic Velocities ◽  
Low Velocity ◽  
Seismic Properties ◽  
Low Resistivity ◽  
Resistivity Model ◽  
Basic Rocks ◽  
Temperature Depth

Data from 20 magnetotelluric stations were used to determine a resistivity‐depth distribution for the crust in western Texas. We computed one‐dimensional models, which adequately explained the apparent resistivities obtained from the elements of a rotated impedance tensor. Descriptions of the method of data processing and model computation are given. The derived model includes an anisotropic, low resistivity layer at depths slightly greater than 20 km. The resistivity model is compared with a seismic velocity interpretation for eastern New Mexico, and the low resistivity layer is inferred to coincide with a zone of low seismic velocity. The base of the low velocity‐low resistivity region occurs at the transition from intermediate to more basic rocks in the crust. The low resistivity values are interpreted as resulting from interstitial fluid. This fluid may cause low seismic velocities and may form a weak region in which continental earthquakes occur. Interstitial water at depth in the crust may be produced by the intersection of the crustal temperature‐depth curve and equilibrium boundaries of hydrothermal reactions.

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

2020 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
Ahmed Lachhab ◽  
El Mehdi Benyassine ◽  
Mohamed Rouai ◽  
Abdelilah Dekayir ◽  
Jean C. Parisot ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Electrical Current ◽  
P Wave ◽  
Low Resistivity ◽  
Refraction Tomography ◽  
Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

scholarly journals Studying the Depth Structure of the Kyrgyz Tien Shan by Using the Seismic Tomography and Magnetotelluric Sounding Methods

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 122
Author(s):  
Irina Medved ◽  
Elena Bataleva ◽  
Michael Buslov
Keyword(s):  
Seismic Tomography ◽  
High Velocity ◽  
Fault Zones ◽  
Magnetotelluric Sounding ◽  
Tien Shan ◽  
High Resistivity ◽  
Low Velocity ◽  
Low Resistivity ◽  
Velocity Models ◽  
Fluid Saturation

This paper presents new results of detailed seismic tomography (ST) on the deep structure beneath the Middle Tien Shan to a depth of 60 km. For a better understanding of the detected heterogeneities, the obtained velocity models were compared with the results of magnetotelluric sounding (MTS) along the Kekemeren and Naryn profiles, running parallel to the 74 and 76 meridians, respectively. We found that in the study region the velocity characteristics and geoelectric properties correlate with each other. The high-velocity high-resistivity anomalies correspond to the parts of the Tarim and Kazakhstan-Junggar plates submerged under the Tien Shan. We revealed that the structure of the Middle Tien Shan crust is conditioned by the presence of the Central Tien Shan microcontinent. It manifests itself as two anomalies lying one below the other: the lower low-velocity low-resistivity anomaly, and the upper high-velocity high-resistivity anomaly. The fault zones, limiting the Central Tien Shan microcontinent, appear as low-velocity low-resistivity anomalies. The obtained features indicate the fluid saturation of the fault zones. According to the revealed features of the Central Tien Shan geological structure, it is assumed that the lower-crustal low-velocity layer can play a significant role in the delamination of the mantle part of the submerged plates.

scholarly journals Delineation of Weathered Layer Using Uphole and Surface Seismic Refraction Methods in Parts of Niger Delta, Nigeria

2021 ◽  
Vol 26 (1) ◽  
pp. 58-66
Author(s):  
Mfoniso Aka ◽  
Okechukwu Agbasi
Keyword(s):  
Niger Delta ◽  
Average Velocity ◽  
Seismic Refraction ◽  
Low Velocity ◽  
Engineering Structures ◽  
Experimental Proof ◽  
Seismic Surveys ◽  
Shot Point ◽  
Weathered Layer ◽  
Velocity Zone

Uphole and surface seismic refraction surveys were carried out in parts of the Niger Delta, Nigeria, to delineate weathering thickness and velocity associated with aweathered layer. A total of twelve uphole and surface seismic refraction surveyswere shot, computed and analyzed. The velocity of the uphole seismic refraction ranged from 344.8 to 680.3 m/s with a thickness of 5.45 to 13.35 m. Surface seismic refraction ranged from 326.6 to 670.2 m/s and 4.30 to 12.0 m, respectively. The average velocity and thickness ranged from 559.6 to 548.0 m/s and 9.43 to 8.63m with differences of 11.6 m/s and 0.83 m respectively. The VW/VS ratios ranged from 0.955 to 1.059. This indicates that the uphole velocity is higher than the surface refraction velocity leading to low VW/VS values. This is a direct experimental proof of a low velocity zone, confirming the weathered nature of the area. The results of both refraction methods are reliable; the differences in surface refraction values are due to shot point offsets. Based on these findings, it is recommended that shots for seismic surveys should be located above 15.0 m in the area to delineate the effects associated with weathered layers to ensure that will be competent to withstand engineering structures.  

Occurrence of cotton herbicides and insecticides in playa lakes of the High Plains of West Texas

2000 ◽  
Vol 248 (2-3) ◽  
pp. 189-200 ◽  
Author(s):  
E.M Thurman ◽  
K.C Bastian ◽  
Tony Mollhagen
Keyword(s):  
High Plains ◽  
Playa Lakes ◽  
West Texas

Quest for Fluid Flow along the Gloria Fault – First results of R/V Meteor expedition 162

2020 ◽  
Author(s):  
Christian Hensen ◽  
Pedro Terrinha ◽  
Joāo Duarte ◽  
Norbert Kaul ◽  
Mark Schmidt ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Seismic Refraction ◽  
Plate Boundary ◽  
Thick Layer ◽  
Deep Ocean ◽  
Transform Faults ◽  
Tectonic Processes ◽  
Exchange Processes ◽  
First Results ◽  
Potential Fluid

<p>Vast areas of the deep ocean floor are still insufficiently explored with respect to tectonic processes, exchange processes between the lithosphere and the ocean, and potential deep chemosynthetic energy sources for life. Transform faults and fracture zones, which are dominant seafloor morphological features in the abyssal ocean, deserve specific attention in this regard as they provide potential pathways for fluid recycling. One of them is the Gloria Fault, a unique feature in the Central North Atlantic. It has been the source of large magnitude earthquakes (namely the 1941, M8.4, the second largest instrumental earthquake on a fracture zone) and is a special case of a plate boundary, corresponding to the transform reactivation of an old oceanic fracture zone. Seismic refraction has shown an anomalous layer between normal lower crust and uppermost mantle, possibly a 4 km thick layer of hydrated mantle. We present first results of RV Meteor cruise M162 (March-April 2020) dedicated to the groundtruthing of potential fluid emanation sites.</p>

Geophysical measurements in the region of the Explorer ridge off western Canada

1978 ◽  
Vol 15 (9) ◽  
pp. 1508-1525 ◽  
Author(s):  
R. D. Hyndman ◽  
G. C. Rogers ◽  
M. N. Bone ◽  
C. R. B. Lister ◽  
U. S. Wade ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Geothermal Heat ◽  
Juan De Fuca Plate ◽  
The North ◽  
The Pacific ◽  
Ocean Bottom Seismometers ◽  
Seismic Reflection Profiles

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.

scholarly journals Investigation of the 1727 Newbury, Massachusetts, USA, earthquake using LiDAR imagery and P-wave velocity tomography

2018 ◽  
pp. 267-283
Author(s):  
Ronald T. Marple ◽  
James D. Hurd, Jr. ◽  
Lanbo Liu ◽  
Seth Travis ◽  
Robert J. Altamura
Keyword(s):  
Wave Velocity ◽  
New Hampshire ◽  
Seismic Refraction ◽  
Surface Expression ◽  
P Wave ◽  
Light Detection And Ranging ◽  
Low Velocity ◽  
P Wave Velocity ◽  
Velocity Tomography ◽  
Velocity Zone

High-resolution LiDAR (light detection and ranging) images of northeastern Massachusetts and southeastern New Hampshire reveal a 10-km-long, NW-SE-oriented topographic lineament in northeastern Massachusetts that we interpret to be the surface expression of a SW-dipping thrust fault along which the 1727 Newbury, Massachusetts, earthquake occurred. The Newburyport lineament coincides with the northeast edge of a 10-kmlong, NW-SE-oriented ridge, herein named Merrimack ridge, that parallels the NW-SE-trending segment of the Merrimack River downstream from where it bends 90° to the southeast. The northwestern end of the Newburyport lineament coincides with a 1-km-long, ~7- to 15-m-high, NE-facing Newburyport scarp that is located just south of the bend in the river. The Newburyport lineament also parallels the NW-SE-oriented nodal planes of the focal mechanism that was generated for the 1999 Amesbury, Massachusetts, earthquake. A P-wave velocity tomographic model generated from a seismic-refraction profile across the Newburyport scarp shows a ~40-m-wide low-velocity zone dipping ~41° SW. Velocities along this zone decrease 15–50%, which suggests that the Newburyport lineament is associated with the surface expression of a SW-dipping brittle fault zone. The LiDAR images also revealed three other NW-SE-trending lineaments in the study area.

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