scholarly journals Scattering images from autocorrelation functions of P-wave seismic velocity images: the case of Tenerife Island (Canary Islands, Spain)

2018 ◽  
Vol 80 (3) ◽  
Author(s):  
A. García-Yeguas ◽  
A. Sánchez-Alzola ◽  
L. De Siena ◽  
J. Prudencio ◽  
A. Díaz-Moreno ◽  
...  
Keyword(s):  
Canary Islands ◽  
Seismic Velocity ◽  
P Wave ◽  
Autocorrelation Functions ◽  
Tenerife Island ◽  
Velocity Images

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.

The relationship between Vs, Vp, density and depth based on PS-logging data at K-NET and KiK-net sites

2021 ◽  
Author(s):  
Fumiaki Nagashima ◽  
Hiroshi Kawase
Keyword(s):  
Standard Deviation ◽  
Seismic Velocity ◽  
Saturated Soil ◽  
P Wave ◽  
Soil Types ◽  
Depth Range ◽  
Velocity Inversion ◽  
Velocity Models ◽  
Regression Curves ◽  
Ps Logging

Summary P-wave velocity (Vp) is an important parameter for constructing seismic velocity models of the subsurface structures by using microtremors and earthquake ground motions or any other geophysical exploration data. In order to reflect the ground survey information in Japan to the Vp structure, we investigated the relationships among Vs, Vp, and depth by using PS-logging data at all K-NET and KiK-net sites. Vp values are concentrated at around 500 m/s and 1,500 m/s when Vs is lower than 1,000 m/s, where these concentrated areas show two distinctive characteristics of unsaturated and saturated soil, respectively. Many Vp values in the layer shallower than 4 m are around 500 m/s, which suggests the dominance of unsaturated soil, while many Vp values in the layer deeper than 4 m are larger than 1,500 m/s, which suggests the dominance of saturated soil there. We also investigated those relationships for different soil types at K-NET sites. Although each soil type has its own depth range, all soil types show similar relationships among Vs, Vp, and depth. Then, considering the depth profile of Vp, we divided the dataset into two by the depth, which is shallower or deeper than 4 m, and calculated the geometrical mean of Vp and the geometrical standard deviation in every Vs bins of 200 m/s. Finally, we obtained the regression curves for the average and standard deviation of Vp estimated from Vs to get the Vp conversion functions from Vs, which can be applied to a wide Vs range. We also obtained the regression curves for two datasets with Vp lower and higher than 1,200 m/s. These regression curves can be applied when the groundwater level is known. In addition, we obtained the regression curves for density from Vs or Vp. An example of the application for those relationships in the velocity inversion is shown.

Seismic tomographic interpretation of Paleozoic sedimentary sequences in the southeastern North Sea

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. R45-R56 ◽  
Author(s):  
Lars Nielsen ◽  
Hans Thybo ◽  
Martin Glendrup
Keyword(s):  
North Sea ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
P Wave ◽  
Wide Angle ◽  
North German Basin ◽  
Sedimentary Sequences ◽  
The North ◽  
Crystalline Crust ◽  
German Basin

Seismic wide-angle data were recorded to more than 300-km offset from powerful airgun sources during the MONA LISA experiments in 1993 and 1995 to determine the seismic-velocity structure of the crust and uppermost mantle along three lines in the southeastern North Sea with a total length of 850 km. We use the first arrivals observed out to an offset of 90 km to obtain high-resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust. Seismic tomographic traveltime inversion reveals 2–8-km-thick Paleozoic sedimentary sequences with P-wave velocities of 4.5–5.2 km/s. These sedimentary rocks are situated below a Mesozoic-Cenozoic sequence with variable thickness: ∼2–3 km on the basement highs, ∼2–4 km in the Horn Graben and the North German Basin, and ∼6–7 km in the Central Graben. The thicknesses of the Paleozoic sedimentary sequences are ∼3–5 km in the Central Graben, more than 4 km in the Horn Graben, up to ∼4 km on the basement highs, and up to 8 km in the North German Basin. The Paleozoic strata are clearly separated from the shallower and younger sequences with velocities of ∼1.8–3.8 km/s and the deeper crystalline crust with velocities of more than 5.8–6.0 km/s in the tomographic P-wave velocity model. Resolution tests show that the existence of the Paleozoic sediments is well constrained by the data. Hence, our wide-angle seismic models document the presence of Paleozoic sediments throughout the southeastern North Sea, both in the graben structures and in deep basins on the basement highs.

scholarly journals Crustal velocity structure of the Apennines (Italy) from P-wave travel time tomography

1996 ◽  
Vol 39 (6) ◽  
Author(s):  
C. Chiarabba ◽  
A. Amato
Keyword(s):  
Velocity Structure ◽  
P Wave ◽  
Depth Interval ◽  
Low Velocity ◽  
Data Set ◽  
Arrival Times ◽  
Velocity Anomaly ◽  
Minimum Number ◽  
Velocity Images ◽  
Lower Crustal

In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy), focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data) we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km) in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

Reliability Assessment of Tunnel Based on P -Wave Seismic Velocity

2018 ◽  
Vol 18 (11) ◽  
pp. 06018030
Author(s):  
Xiao-Ping Zhou ◽  
Xiao-Cheng Huang ◽  
Jin-Xin Li
Keyword(s):  
Seismic Velocity ◽  
Reliability Assessment ◽  
P Wave

scholarly journals Noise-based ballistic wave passive seismic monitoring. Part 1: body waves

2020 ◽  
Vol 221 (1) ◽  
pp. 683-691 ◽  
Author(s):  
F Brenguier ◽  
R Courbis ◽  
A Mordret ◽  
X Campman ◽  
P Boué ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Noise Source ◽  
Seismic Monitoring ◽  
Body Waves ◽  
P Wave ◽  
New Technique ◽  
Apparent Velocity ◽  
Near Surface ◽  
Velocity Increase ◽  
Passive Seismic

SUMMARY Unveiling the mechanisms of earthquake and volcanic eruption preparation requires improving our ability to monitor the rock mass response to transient stress perturbations at depth. The standard passive monitoring seismic interferometry technique based on coda waves is robust but recovering accurate and properly localized P- and S-wave velocity temporal anomalies at depth is intrinsically limited by the complexity of scattered, diffracted waves. In order to mitigate this limitation, we propose a complementary, novel, passive seismic monitoring approach based on detecting weak temporal changes of velocities of ballistic waves recovered from seismic noise correlations. This new technique requires dense arrays of seismic sensors in order to circumvent the bias linked to the intrinsic high sensitivity of ballistic waves recovered from noise correlations to changes in the noise source properties. In this work we use a dense network of 417 seismometers in the Groningen area of the Netherlands, one of Europe's largest gas fields. Over the course of 1 month our results show a 1.5 per cent apparent velocity increase of the P wave refracted at the basement of the 700-m-thick sedimentary cover. We interpret this unexpected high value of velocity increase for the refracted wave as being induced by a loading effect associated with rainfall activity and possibly canal drainage at surface. We also observe a 0.25 per cent velocity decrease for the direct P-wave travelling in the near-surface sediments and conclude that it might be partially biased by changes in time in the noise source properties even though it appears to be consistent with complementary results based on ballistic surface waves presented in a companion paper and interpreted as a pore pressure diffusion effect following a strong rainfall episode. The perspective of applying this new technique to detect continuous localized variations of seismic velocity perturbations at a few kilometres depth paves the way for improved in situ earthquake, volcano and producing reservoir monitoring.

scholarly journals Density-Depth Profile Determined by Seismic-Refraction Studies: Ice Stream B. West Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 198 ◽  
Author(s):  
S. Anandakrishnan
Keyword(s):  
Shear Wave ◽  
Seismic Velocity ◽  
Austral Summer ◽  
P Wave ◽  
S Wave ◽  
Data Logger ◽  
High Resolution Data ◽  
Ice Stream ◽  
Wave Profiles ◽  
Depth Curve

Detailed seismic short-refraction profiling was conducted on Ice Stream Β (UpB) during the 1983–84 austral summer. A new high-resolution data logger, developed at the University of Wisconsin, recorded both compressional- and shear-wave arrivals. We report here on P-wave and S-wave profiles recorded along a line parallel to the axis of the ice stream. Source-receiver separations up to 720 m yielded seismic velocity-depth curves to below the firn-ice transition zone (slightly greater than 30 m at UpB). For the compressional-wave profile, geophones were separated by 2.5 m, which yielded a velocity-depth curve with a granularity of ∼1 m. The corresponding density-depth curve agrees well with direct density measurements obtained from a core extracted nearby (Alley and Bentley 1988, this volume). Discontinuities in the velocity gradient do not appear at the “critical densities” as they did at Byrd Station, Antarctica, and elsewhere (Kohnen and Bentley 1973 , Robertson and Bentley 1975). Two shear-wave profiles were recorded, both with geophone spacings of 5 m, one with longitudinal polarization (SV) and the other with transverse polarization (SH). There is a marked difference in velocity between the SH and SV waves, particularly in the shallow firn. We suggest that a strong vertical shape-and-bonding fabric in the shallow firn, as observed in cores collected at UpB, would account for this disparity.

Marcellus fracture characterization using P-wave azimuthal velocity attributes: Comparison with production and outcrop data

2015 ◽  
Vol 3 (3) ◽  
pp. SU1-SU15 ◽  
Author(s):  
Tanya L. Inks ◽  
Terry Engelder ◽  
Edward Jenner ◽  
Bruce Golob ◽  
Jacki S. Hocum ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Marcellus Shale ◽  
Azimuthal Velocity ◽  
P Wave ◽  
Published Data ◽  
Seismic Profiles ◽  
Fracture Characterization ◽  
Decline Curve ◽  
Fracture Models ◽  
Well Data

Analysis of two 3D surveys, available well data, published outcrop data and subsurface information, as well as production data available from the state of Pennsylvania, demonstrates that wide-azimuth seismic is sensitive to variations in fracturing at the scale of individual pads or even individual wells. These variations in fracturing begin to explain why production varies significantly, even locally, within the Marcellus Shale gas play. Rose diagrams from quantitative fracture analysis using azimuthal seismic velocity volumes were compared with published data from Appalachian black shale outcrops and subsurface fracture models proposed in various papers to validate the results from subsurface data. These analyses provided insight into the rock fabric and the presence of systematic joints that likely affect production. There was a strong correlation between the low anisotropy and low heterogeneity of anisotropy and high estimated ultimate recovery (EUR). Additionally, interpreted fracture trend azimuths differed between areas of larger gas EUR and areas of smaller gas EUR as defined by decline curve analysis. Some perforations were likely to perform much better than others along the borehole, based on observed heterogeneity in the seismic profiles and map view.

scholarly journals The Local Earthquake Tomography of Erzurum (Turkey) Geothermal Area

2019 ◽  
Vol 23 (3) ◽  
pp. 209-223 ◽  
Author(s):  
Caglar Ozer ◽  
Mehmet Ozyazicioglu
Keyword(s):  
Wave Velocity ◽  
Seismic Velocity ◽  
Three Dimensional ◽  
P Wave ◽  
Geothermal Area ◽  
S Wave ◽  
Velocity Models ◽  
Local Earthquake Tomography ◽  
P Wave Velocity ◽  
Local Earthquake

Erzurum and its surroundings are one of the seismically active and hydrothermal areas in the Eastern part of Turkey. This study is the first approach to characterize the crust by seismic features by using the local earthquake tomography method. The earthquake source location and the three dimensional seismic velocity structures are solved simultaneously by an iterative tomographic algorithm, LOTOS-12. Data from a combined permanent network comprising comprises of 59 seismometers which was installed by Ataturk University-Earthquake Research Center and Earthquake Department of the Disaster and Emergency Management Authority  to monitor the seismic activity in the Eastern Anatolia, In this paper, three-dimensional Vp and Vp/Vs characteristics of Erzurum geothermal area were investigated down to 30 km by using 1685 well-located earthquakes with 29.894 arrival times, consisting of 17.298 P- wave and 12.596 S- wave arrivals. We develop new high-resolution depth-cross sections through Erzurum and its surroundings to provide the subsurface geological structure of seismogenic layers and geothermal areas. We applied various size horizontal and vertical checkerboard resolution tests to determine the quality of our inversion process. The basin models are traceable down to 3 km depth, in terms of P-wave velocity models. The higher P-wave velocity areas in surface layers are related to the metamorphic and magmatic compact materials. We report that the low Vp and high Vp/Vs values are observed in Yedisu, Kaynarpinar, Askale, Cimenozu, Kaplica, Ovacik, Yigitler, E part of Icmeler, Koprukoy, Uzunahmet, Budakli, Soylemez, Koprukoy, Gunduzu, Karayazi, Icmesu, E part of Horasan and Kaynak regions indicated geothermal reservoir.

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