Characterizing an unstable mountain slope using shallow 2D and 3D seismic tomography

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. B241-B256 ◽  
Author(s):  
Bjoern Heincke ◽  
Hansruedi Maurer ◽  
Alan G. Green ◽  
Heike Willenberg ◽  
Tom Spillmann ◽  
...  
Keyword(s):  
Rock Mass ◽  
Seismic Refraction ◽  
P Wave ◽  
Fracture Zones ◽  
Mountain Slope ◽  
Low Field ◽  
P Wave Velocity ◽  
First Arrival ◽  
Mobile Segment ◽  
2D And 3D

As transport routes and population centers in mountainous areas expand, risks associated with rockfalls and rockslides grow at an alarming rate. As a consequence, there is an urgent need to delineate mountain slopes susceptible to catastrophic collapse in a safe and noninvasive manner. For this purpose, we have developed a 3D tomographic seismic refraction technique and applied it to an unstable alpine mountain slope, a significant segment of which is moving at [Formula: see text] toward the adjacent valley floor. First arrivals recorded across an extensive region of the exposed gneissic rock mass have extraordinarily low apparent velocities at short [Formula: see text] to long [Formula: see text] shot-receiver offsets. Inversion of the first-arrival traveltimes produces a 3D tomogram that reveals the presence of a huge volume of very-low-quality rock with ultralow to very low P-wave velocities of [Formula: see text]. These values are astonishingly low compared to the average horizontal P-wave velocity of [Formula: see text] determined from laboratory analyses of intact rocks collected at the investigation site. The extremely low field velocities likely result from the ubiquitous presence of dry cracks, fracture zones, and faults on a wide variety of scales. They extend to more than [Formula: see text] depth over a [Formula: see text] area that encompasses the mobile segment of the mountain slope, which is transected by a number of actively opening fracture zones and faults, and a large part of the adjacent stationary slope. Although hazards related to the mobile segment have been recognized since the last major rockslides affected the mountain in 1991, those related to the adjacent low-quality stationary rock mass have not.

Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico

1984 ◽  
Vol 74 (4) ◽  
pp. 1263-1274
Author(s):  
Lawrence H. Jaksha ◽  
David H. Evans
Keyword(s):  
New Mexico ◽  
Wave Velocity ◽  
Lower Crust ◽  
Seismic Waves ◽  
Seismic Refraction ◽  
Velocity Model ◽  
P Wave ◽  
Uppermost Mantle ◽  
P Wave Velocity ◽  
Crustal Thinning

Abstract A velocity model of the crust in northwestern New Mexico has been constructed from an interpretation of direct, refracted, and reflected seismic waves. The model suggests a sedimentary section about 3 km thick with an average P-wave velocity of 3.6 km/sec. The crystalline upper crust is 28 km thick and has a P-wave velocity of 6.1 km/sec. The lower crust below the Conrad discontinuity has an average P-wave velocity of about 7.0 km/sec and a thickness near 17 km. Some evidence suggests that velocity in both the upper and lower crust increases with depth. The P-wave velocity in the uppermost mantle is 7.95 ± 0.15 km/sec. The total crustal thickness near Farmington, New Mexico, is about 48 km (datum = 1.6 km above sea level), and there is evidence for crustal thinning to the southeast.

A Measurement of Seismic Anistropy in the Northeast Pacific

1971 ◽  
Vol 8 (9) ◽  
pp. 1056-1064 ◽  
Author(s):  
C. E. Keen ◽  
D. L. Barrett
Keyword(s):  
Seismic Refraction ◽  
Maximum Velocity ◽  
Mean Value ◽  
Ocean Basin ◽  
P Wave ◽  
Sea Floor ◽  
P Wave Velocity ◽  
The Pacific ◽  
Magnetic Lineations ◽  
Sea Floor Spreading

A seismic refraction experiment was conducted in the Pacific Ocean basin, off the coast of British Columbia, Canada. The purpose of these measurements was to obtain an estimate of the anisotropy of the mantle P-wave velocity in the area and to relate this parameter to the direction of sea floor spreading. The results show that the crustal structure is similar to that measured elsewhere in the Pacific basin. Significant anisotropy of the mantle rocks is observed; the direction in which the maximum velocity occurs being 107° and the change of velocity, about 8% of the mean value, 8.07 km/s. The direction of maximum velocity does not coincide exactly with the direction of sea floor spreading, 090°, inferred from magnetic lineations.

Field trials of a seismoelectric method for detecting massive sulfides

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 365-373 ◽  
Author(s):  
Anton W. Kepic ◽  
Michael Maxwell ◽  
R. Don Russell
Keyword(s):  
Electromagnetic Radiation ◽  
Acoustic Waves ◽  
Seismic Energy ◽  
Field Trials ◽  
P Wave ◽  
Massive Sulfides ◽  
P Wave Velocity ◽  
Electromagnetic Emissions ◽  
First Arrival ◽  
Exploration Tool

An underground test of a seismoelectric prospecting method for massive sulfides was performed at the Mobrun Mine (Rouyn‐Noranda, Quebec) in June 1991. The method is based upon the conversion of seismic energy to high‐frequency pulses of electromagnetic radiation by sulfide minerals. The delay between shot detonation and detection of the electromagnetic radiation gives a one‐way traveltime for the acoustic wave to reach the zone of seismoelectric conversion, which when combined with P‐wave velocity allows the shot‐to‐ore zone distance to be calculated. A 0.22-kg explosive charge located within 50 m of the orebody provided the seismic excitation, and the resulting electromagnetic emissions were received by electric dipole and induction‐coil antennas. First‐arrival information from a 35‐shot survey above an orebody, the 1100 lens, provides firm evidence that short duration pulses of electromagnetic radiation are produced by the passage of acoustic waves through the orebody. The survey also demonstrated that seismoelectric conversions could be induced at shot‐to‐orebody distances of 50 m and detected at distances of up to 150 m from the orebody. Areas of seismoelectric conversion are highlighted in sections produced by plotting the position of seismic wavefronts during signal reception. The sections show anomalies that correlate with the known structure and location of the orebody and demonstrate the potential of using this seismoelectric phenomenon as an exploration tool.

Geophysical mapping of gypsum for exploration of reserves in the Nong Bua area of Thailand

2020 ◽  
pp. qjegh2019-180
Author(s):  
Rungroj Arjwech ◽  
Mark E. Everett ◽  
Sakhon Saengchomphu ◽  
Kittipong Somchat ◽  
Potpreecha Pondthai
Keyword(s):  
Electrical Resistivity ◽  
Construction Projects ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Raw Material ◽  
P Wave ◽  
The Core ◽  
Micro Cracks ◽  
P Wave Velocity ◽  
Increasing Demand

The increasing demand for gypsum as a raw material for construction projects motivates exploration for additional reserves. Electrical resistivity tomography (ERT) and seismic refraction geophysical methods, augmented with borehole and laboratory measurements on core samples, are used here to delineate the top, bottom and lateral boundaries of an important gypsum ore deposit in Thailand, an economically developing region. The gypsum-bearing formation is found throughout the study area to have an irregular upper boundary on account of karstic dissolution processes. The deeper transition from gypsum to anhydrite, however, is not constrained by the measurements. The P-wave velocity measured in the field is consistent with the core specimen measurements. The electrical resistivity of the core specimens, however, is substantially higher than the values measured in the field. The specimen measurements may depend on the presence of micro cracks, whereas electrical resistivity in the field may be affected by the enclosing clay-rich materials.

Stratigraphic Analysis with Refraction Tomography

2019 ◽  
Vol 25 (3) ◽  
pp. 245-254
Author(s):  
Peter J. Hutchinson ◽  
Maggie H. Tsai
Keyword(s):  
Seismic Refraction ◽  
High Energy ◽  
P Wave ◽  
Tidal Channels ◽  
Near Surface ◽  
Precambrian Rocks ◽  
Stratigraphic Analysis ◽  
P Wave Velocity ◽  
Refraction Tomography ◽  
Near Shore

ABSTRACT Near-surface seismic refraction tomography imaged the basal contact of the Upper Cambrian silica-rich Mount Simon Formation with that of the underlying Precambrian granite in central Wisconsin. The discrimination between the Mount Simon and underlying non-conformable contact with Precambrian rocks was based upon a p-wave velocity of 1,700 m/s. Refraction tomography imaged deep, broad tidal channels within the Mount Simon consistent with the inference that Mount Simon was deposited in a high-energy near-shore, probably fluvial environment. The Mount Simon is an arenite that has high commercial value.

Crustal structures across the young and oblique North-eastern Gulf of Aden margin

2020 ◽  
Author(s):  
Louise Watremez ◽  
Sylvie Leroy ◽  
Elia d'Acremont ◽  
Stéphane Rouzo
Keyword(s):  
Seismic Waves ◽  
Seismic Refraction ◽  
P Wave ◽  
Gulf Of Aden ◽  
S Wave ◽  
Acoustic Basement ◽  
S Waves ◽  
P Wave Velocity ◽  
North Eastern ◽  
Lower Crustal

<p>The Gulf of Aden is a young and active oceanic basin, which separates the south-eastern margin of the Arabian Plate from the Somali Plate. The rifting leading to the formation of the north-eastern Gulf of Aden passive margin started ca. 34 Ma ago when the oceanic spreading in this area initiated at least 17.6 Ma ago. The opening direction (N26°E) is oblique to the mean orientation of the Gulf (N75°E), leading to a strong structural segmentation.</p><p>The Encens cruise (2006) allowed for the acquisition of a large seismic refraction dataset with profiles across (6 lines) and along (3 lines) the margin, between the Alula-Fartak and Socotra-Hadbeen fracture zones, which define a first order segment of the Gulf. P-wave velocity modelling already allowed us to image the crustal thinning and the structures, from continental to oceanic domains, along some of the profiles. A lower crustal intermediate body is observed in the Ashawq-Salalah segment, at the base of the transitional and oceanic crusts. The nature of this intermediate body is most probably mafic, linked to a post-rift thermal anomaly. The thin (1-2 km) sediment layer in the study area allows for a clear conversion of P-waves to S-waves at the top basement. Thus, most seismic refraction records show very clear S-wave arrivals.</p><p>In this study, we use both P-wave and S-wave arrivals to delineate the crustal structures and segmentation along and across the margin and add insight into the nature of the rocks below the acoustic basement. P-wave velocity modelling allows for the delineation of the structure variations across and along the margin. The velocity models are used as a base for the S-wave modelling, through the definition of Poisson’s ratios in the different areas of the models. Picking and modelling of S-wave arrivals allow us to identify two families of converted waves: (1) seismic waves converted at the basement interface on the way up, just before arriving to the OBS and (2) seismic waves converted at the basement on the way down, which travelled into the deep structures as S-waves. The first set of arrivals allows for the estimation the S-wave velocities (Poisson’s ratio) in the sediments, showing that the sediments in this area are unconsolidated and water saturated. The second set of arrivals gives us constraints on the S-wave velocities below the acoustic basement. This allows for an improved mapping of the transitional and oceanic domains and the confirmation of the mafic nature of the lower crustal intermediate body.</p>

Anisotropy and fracture zones about a geothermal well from P‐wave velocity profiles

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 25-36 ◽  
Author(s):  
P. C. Leary ◽  
T. L. Henyey
Keyword(s):  
High Resolution ◽  
P Wave ◽  
Basement Rock ◽  
Fracture Zones ◽  
Shoot Method ◽  
Velocity Anisotropy ◽  
Geothermal Well ◽  
P Wave Velocity ◽  
Angle Fracture ◽  
Beaver County

The feasibility of locating fracture zones and estimating their crack parameters was examined using an “areal well shoot” method centered on Utah State Geothermal Well 9‐1, Beaver County, Utah. High‐resolution traveltime measurements were made between a borehole sensor and an array of shotpoints distributed radially and azimuthally about the well. The directional dependence of velocity in the vicinity of the well was investigated by comparing traveltimes from different azimuths. Velocity anisotropy was detected; this condition is consistent with, but not required by, the existence of fractures in the basement rock having orientations subparallel to the latest episode of local faulting. The interpretation is complicated by a variable thickness of overburden around the well. Traveltime delays also suggest the presence of a low‐angle fracture zone intersecting the well at a depth of ∼1 500 ft.

scholarly journals Estimation of Geodynamic Properties using Seismic Techniques at a Steel Rolling Factory, Northwestern Gulf of Suez, Egypt

2020 ◽  
Vol 8 (6) ◽  
pp. 1785-1794
Keyword(s):  
Wave Velocity ◽  
Seismic Waves ◽  
Seismic Refraction ◽  
Industrial Area ◽  
P Wave ◽  
Gulf Of Suez ◽  
S Wave ◽  
P Waves ◽  
Steel Rolling ◽  
P Wave Velocity

The objective of the current investigations is to estimate the dynamic geotechnical properties necessary for evaluating the conditions of the subsurface in order to make better decisions for economic and safe designs of the proposed structures at a Steel Rolling Factory, Ataqa Industrial Area, Northwestern Gulf of Suez, Egypt. To achieve this purpose, four seismic refraction profiles were conducted to measure the velocity of primary seismic waves (P-waves) and four profiles were conducted using Multichannel Analysis of Surface Waves (MASW) technique in the same locations of refraction profiles to measure the velocity of shear waves (S-waves). SeisImager/2D Software Package was used in the analysis of the measured data. Data processing and interpretation reflect that the subsurface section in the study area consists of two layers, the first layer is a thin surface layer ranges in thickness from 1 to 4 meters with P-wave velocity ranges from 924 m/s to 1247 m/s and S-wave velocity ranges from 530 m/s to 745 m/s. The second layer has a P-wave velocity ranges from 1277 m/s to 1573 m/s and the S-wave velocity ranges from 684 m/s to 853 m/s. Geotechnical parameters were calculated for both layers. Since elastic moduli such as Poisson’s ratio, shear modulus, Young’s modulus, and bulk’s modulus were calculated. Competence scales such as material index, stress ratio, concentration index, and density gradient were calculated also. In addition, the ultimate and allowable bearing capacities

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