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1

Landslide survey at Cam Mountain (An Giang, Vietnam) by seismic refraction and GPR methods

Nguyen Giang Van, Nguyen Dung Quang, Le Thanh Ngoc

Archives of Mining Sciences

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2023

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Vol. 68, no. 4

603--620

EN

Cam Mountain in An Giang Province, Vietnam, is a granite peak that is severely fractured and eroded on its slopes and summit. Trees cover the top of the mountain and around the side of the mountain. The roads are the primary means of transportation for indigenous people and tourists daily. Recently, there has been a phenomenon of large-sized boulders rolling down from the top of the mountain, causing an accident and killing tourists. To investigate the internal causes of landslides on a 2.3 km road stretch, geophysical profiles using GPR and seismic refraction methods were conducted to clarify the current status of geological structures beneath the road surface. The refractive seismic data analysis revealed four distinct layers based on elastic wave propagation velocity. Velocity values range from 1000 to 3000 m/s for the 2 upper layers corresponding to the weathered, broken, and highly fractured rock layers and in the lower 2 layers from 3000 to more than 4500 m/s, respectively corresponding to less fractured rock on the depth of more than 50 m. According to GPR data, the structural cross-section to an average depth of 30 m is a more complex picture. Detected 6 layers with different degrees of fracture cracking and showing different structural zones. In a few places are the drainage creeks from the mountain. These places need to be monitored regularly to have a basis for predicting landslides and rockfalls in the area of Cam Mountain. Landslides occur in geological rocks which are of different ages: claystone, mudstone, siltstone, shale, or marlstone. The rock-falls occur in more compact rocks: metamorphic or igneous rocks.

2

Selected aspects of modern seismic imaging and near-surface velocity model building in the area of Carpathian fold and thrust belt

Dalętka Andrzej Michał

Geology, Geophysics and Environment

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2021

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Vol. 47, no. 2

71--93

EN

Despite the increasing technological level of the reflection seismic method, the imaging of fold and thrust belts remains a demanding task, and usually leaves some questions regarding the dips, the shape of the subthrust structures or the most correct approach to velocity model building. There is no straightforward method that can provide structural representation of the near-surface geological boundaries and their velocities. The interpretation of refracted waves frequently remains the only available technique that may be used for this purpose, although one must be aware of its limitations which appear in the complex geological settings. In the presented study, the analysis of velocity values obtained in the shallow part of Carpathian orogenic wedge by means of various geophysical methods was carried out. It revealed the lack of consistency between the results of 3D refraction tomography and both the sonic log and uphole velocities. For that reason, instead of the industry-standard utilization of tomography, a novel, geologically-consistent method of velocity model building is proposed. In the near-surface part, the uphole velocities are assigned to the formations, documented by the surface geologic map. Interpreted time-domain horizons, supplemented by main thrusts, are used to make the velocity field fully-compatible with the litho-stratigraphic units of the Carpathians. The author demonstrates a retrospective overview of seismic data imaging in the area of the Polish Carpathian orogenic wedge and discusses the most recent global innovations in seismic methodology which are the key to successful hydrocarbon exploration in fold and thrust regions.

3

Zastosowanie MASW i sejsmiki refrakcyjnej do badania anizotropii prędkości w masywie skalnym

Stan-Kłeczek I., Marciniak A.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

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2016

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nr 93

123--131

PL

Jedną z najbardziej charakterystycznych cech skał jest występowanie w nich spękań o różnym kształcie i wypełnieniu. Te nieciągłości powierzchni mają istotny wpływ na właściwości fizyczne skał. Efektem uprzywilejowania określonych kierunków jest anizotropia właściwości sprężystych masywu, w szczególności zaś anizotropia prędkości fal sejsmicznych, charakteryzująca się tym, że prędkość fal w kierunku prostopadłym do biegu spękań jest mniejsza niż w kierunku równoległym. Prezentowane badania prowadzone były w kopalni dolomitu Podleśna. W celu określenia związku pomiędzy szczelinowatością a prędkością fal sejsmicznych wykorzystano metodę sejsmiki refrakcyjnej (RFR) oraz wielokanałową analizę fal powierzchniowych (MASW). Otrzymane wartości prędkości fal sejsmicznych dla azymutów 0, 30, 60, 90, 120 i 150° porównano z kierunkami systemów spękań pomierzonych kompasem geologicznym. Do opisu kierunkowych rozkładów prędkości wykorzystano również rachunek tensorowy, który pozwala na odwzorowanie anizotropii sejsmicznej. Uzyskane maksima prędkości dla fali P pomierzonej za pomocą sejsmiki refrakcyjnej, jak i wartości prędkości fali S uzyskanej metodą MASW pokazują korelację z kierunkami głównych systemów spękań pomierzonych kompasem geologicznym, co pozwala na wykorzystanie wymienionych technik do badania szczelinowatości masywów skalnych.

EN

One of the most characteristic features of rocks is occurrence different kinds and sizes of cracks. These surface discontinuities have an important influence on the physical properties of rocks, especially on seismic wave velocity. The preferred orientation of crack systems involves the anisotropy of seismic wave velocity. It is characterized by a wave velocity that is smaller in the direction perpendicular to the crack plane than in the parallel direction. The presented study was carried out in the Triassic dolomite quarry “Podleśna” located in the South of Poland. The seismic anisotropy of rock mass was measured using the seismic refraction method (RFR) and Multichannel Analysis of Surface Wave (MASW). The research was conducted along oriented seismic profiles (0°, 30°, 60°,90°,120° i 150°) and compared with main crack systems measured on a geological compass. Tensor calculus was also applied to describe the directional distribution of seismic wave velocity. The obtained maximal value of seismic P-wave velocity (RFR) and S-wave velocity (MASW) show very good agreement with the directions of the main crack systems which allow these methods to be used to study of fracturing.

4

Zastosowanie metod geofizycznych do rozpoznania powierzchni stropowej gruntów słabo przepuszczalnych oraz wyznaczenia stref rozluźnienia w korpusie zapory ziemnej

Mieszkowski R., Kowalczyk S., Barański M., Szczepański T.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

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2014

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nr 86

167--180

PL

Metody geofizyczne wykorzystywane jako badania uzupełniające przy badaniu podłoża umożliwiają ocenę jakościową zmienności warunków gruntowych w strefie przypowierzchniowej. Informacje te są szczególnie istotne w monitoringu podłoża budowli hydrotechnicznych. W artykule przedstawiono badania geofizyczne wykonane w rejonie zapory ziemnej, mające na celu wskazanie miejsc rozluźnienia gruntów w obrębie zapory oraz określenie głębokości stropu gruntów spoistych występujących pod zaporą. Zastosowano metody: tomografii elektrooporowej (ERT), georadarową (GPR), sejsmiki refrakcyjnej, dające dwuwymiarowy obraz zmian fizycznych w ośrodku oraz sejsmikę fal powierzchniowych - Continuous Surface Wave System (CSWS), dzięki której otrzymano profil 1D parametrów sztywności ośrodka w punkcie pomiarowym. Opierając się na rezultatach badan ERT oraz sejsmice refrakcyjnej, odniesione do danych z wierceń, opracowano mapę powierzchni stropowej gruntów słabo przepuszczalnych. Anomalie uzyskane w wyniku interpretacji przeprowadzonych badań geofizycznych pozwoliły na oszacowanie stref rozluźnienia gruntu, które mogą być wywołane procesem sufozji. Zaobserwowane anomalie, na wybranych obszarach, zostały skorelowane z wierceniami oraz sondowaniami statycznymi (CPT), co pozwoliło na zrealizowanie postawionego celu oraz sformułowanie wniosku, że rozkład stref rozluźnienia gruntów oraz zwiększonego przepływu wód gruntowych stwarza zagrożenie dla stateczności korpusu zapory.

EN

Geophysical methods used as a complementary survey in the investigation of substrate allow for a qualitative assessment of the lateral variability of ground conditions in the near surface zone. They can also permit evaluation of the vertical variation of ground conditions. Such information is particularly important in monitoring the substratum of hydrotechnical engineering constructions. This article presents the geophysical surveys carried out in the area of an earth dam in order to identify places of relaxation of soils within the dam, as well as to determine the depth of the roof of cohesive soils occurring under the dam. The following methods were used: Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), seismic refraction (providing a two-dimensional image of the physical changes in the medium), and surface wave seismic - Continuous Surface Wave System (CSWS) used together with Spectral Analysis of Surface Waves (SASW). The last method made it possible to analyze the distribution of the stiffness parameters of the medium at the measuring point. Based on the results of ERT studies and seismic refraction, referring to drilling data, a map of the roof surface of cohesive soils was developed. Anomalies identified in the geophysical studies made it possible to estimate the relaxation zone of the soil that could be caused by a process of suffosion. The observed anomalies in selected areas were correlated with drilling and Cone Penetration Testing (CPT), which allowed the completion of the pursued objective and to draw conclusions for the whole dam.

5

Ocena przydatności obszaru pogórniczego do celów budowlanych na podstawie badań sejsmicznych

Matuła R., Czaja K.

Wiadomości Górnicze

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2014

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R. 65, nr 9

486--489

PL

W artykule opisano przykład zastosowania sejsmiki refrakcyjnej do potrzeb rozpoznania terenu pogórniczego. Akwizycję danych przeprowadzono przy użyciu 48-kanałowego sejsmografu. Źródłem fali był lekki wibrator akustyczny. Na podstawie fali refrakcyjnej obliczono głębokość zalegania stropu kredy i rozkład prędkości fali P w jej obrębie. Do tego celu posłużono się funkcją GRM pakietu Seismic Unix, na której podstawie wyznaczono wspomniane wartości dla profilu R1 i R2. Analizując wyniki użycia funkcji GRM, można stwierdzić, iż średnia prędkość w części stropowej podłoża, przypadku obu profili oscyluje w granicy 1800 m/s. Oznacza to, że podłoże wykazuje zwięzłość wystarczającą, do wykorzystania opisywanego obszaru do celów budowlanych.

EN

The article describes an example of the application of seismic refraction for the needs of exploration of a post-mining area. Data acquisition was performed using a 48-channel seismograph. A light acoustic vibrator was the source of a wave. On the basis of refraction wave the depth of bedding of the chalk's roof and P-wave velocity distribution within it was calculated. GRM Seismic Unix function was used for this purpose, on the basis of which the mentioned values were determined for the profiles R1 and R2. Analyzing the results of the use of GRM function, it can be concluded that the average velocity in the roof part of substrate for both profiles oscillate within the limit of 1800 m/s. This means that the substrate indicates a satisfactory compactness of the described area to be used for the construction purposes.

6

Influence of seismic wave frequency on the quality of the landslide surface exploration in the light of numerical modeling

Pilecki R.

Geoinformatica Polonica

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2013

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T. 12

73--84

EN

The paper summarizes results of numerical analysis of source frequency influence on the quality of seismic recognition of the landslide failure surface. Numerical simulation was carried out for the seismic refraction method in two-dimensional model of landslide. The analyzed model was constructed on the basis of geological engineering model of typical landslide conditions in the Carpathian flysch located in the Mucharz village area. Numerical analysis allowed us to obtain the optimal frequency for recognition of surface failure location. It was shown that frequency above 50 Hz is the most promising in measurements conditions. It was proved that seismic measurements allowed us to get more adequate results in detecting discontinuity borders in comparison with theoretical resolution. Numerical computations were realized by finite difference method using FLAC 5.0 software and their interpretations using Plotrefa software.

PL

W artykule przedstawiono wyniki numerycznej analizy wpływu częstotliwości fali sejsmicznej na dokładność sejsmicznego rozpoznania powierzchni poślizgu osuwiska. W tym celu opracowano metodykę numerycznej symulacji sej-smicznych pomiarów refrakcyjnych. Metodykę tą zweryfikowano dla budowy i właściwości osuwiska w miejscowości Mucharz w Karpatach fliszowych. Analiza numeryczna pozwoliła na ustalenie optymalnej częstotliwości dla uzyskania możliwie dobrego rozpoznania położenia powierzchni poślizgu osuwiska w przyjętych warunkach geologiczno-inżynierskich. Wykazano, że najkorzystniejsze są częstotliwości powyżej 50 Hz w analizowanym zakresie do 120 Hz. Pokazano, że pomiary sejsmiczne pozwalają na dokładniejsze wyznaczenie granic nieciągłości, niż to wynika z teoretycznej rozdzielczości. Obliczenia numeryczne sejsmogramów wykonano programem FLAC w wersji 5.0 (prod. Itasca, USA), a ich interpretację programem Plotrefa (prod. Geometrix, USA).

7

Seismic model and geological interpretation of the basement beneath the Doupovske Hory Volcanic Complex (NW Czech Republic)

Valenta J., Broz M., Malek J., Mlcoch B., Rapprich V., Skacelova Z.

Acta Geophysica

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2011

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Vol. 59, no. 3

597-617

EN

The Doupovske Hory Volcanic Complex (DHVC) is the bestpreserved large volcanic suite of the Cenozoic intraplate volcanism in the Bohemian Massif. However, many uncertainties remain in the geological setting of its basement. In summer 2008, two seismic refraction profiles ran across this area to reveal the depth of the volcanic rocks and the underlying geological structure. A high-velocity body was detected beneath the central part of the DHVC at depths of about -500 m a.s.l., inclined to the NW at an angle of about 45°. This body is most likely formed by the basic and ultrabasic rocks (amphibolites, eclogites, serpentinites, metagabbros) of the Equivalent of the Marianske Lazne Complex (EMLC). Subvolcanic rocks of the DIC penetrating these basic and ultrabasic metamorphic rocks have very similar physical properties. Therefore, intrusive body of the Doupov Intrusive Complex (DIC) can be hardly distinguished from rocks of the EMLC by seismic refraction investigation.

8

Relationships between water flow rate and geophysical measurements in an alluvial aquifer

Sénéchal P., Sénéchal G.

Acta Geophysica

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2010

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Vol. 58, no. 1

83-95

EN

Our study focuses on the potential usefulness of surface geophysical data to constrain the water content within an alluvial aquifer. On a study area where two wells have been drilled, we have performed several geophysical measurements, including ground penetrating radar, DC resistivity prospecting, seismic refraction survey and magnetic resonance soundings. From these data, we estimated several parameters, namely, the water height in the deposits, the effective porosity, the water content, the permeability, and the transmissivity of alluvial deposits. These physical parameters allow us to characterize the alluvial deposits in order to constrain the estimation of the potential water flow. The lithology and water flow rate known from the wells enabled us to compare geophysical results obtained in a high water flow rate zone to those in a low water flow rate zone. Correlation has been found between the water flow rate observed in both wells and the geophysical data obtained in the vicinity of these wells.

9

DC resistivity and seismic refraction survey across the SE margin of Lake Ngami, NW Botswana

Shemang E.M., Molwalefhe L.N.

Acta Geophysica

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2009

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Vol. 57, no. 3

728-742

EN

Seismic refraction survey and DC resistivity measurements were made across the margin of the Lake Ngami. The structure and stratigraphy at the lake were determined. High resolution aeromagnetic data showed a prominent anomaly coinciding with the Kunyere Fault. Estimated depths to magnetic sources are increasing towards the lake. Two velocity layers were mapped. The top layer (500 m/s) is thin outside the lake and thicker inside the lake. The underlying layer (3125 m/s) has undeterminable thickness. Resistivity sounding results inside the lake showed that the low velocity layer has four sub-units: dry hard clays; diatomaceous earth; soft clays interlayered with silts; and wet whitish clays interlayered with silts. Normal faults were mapped along the profile with a total displacement up to 50 m. The results of the study indicate that the formation of the Lake Ngami basin was structurally controlled and probably initiated by the tectonics of the Okavango Rift Zone.

10

Simulating time-histories and pseudo-spectral accelerations from the 1992 Cairo earthquake at the proposed El-Fayoum New City Site, Egypt

Abd El-Aal A.E.K.

Acta Geophysica

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2008

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Vol. 56, no. 4

1025-1042

EN

El-Fayoum New City represents one of the new urban settlements that are recently erected all over Egypt. Because seismic recordings are not available, I used the stochastic method to simulate the largest damaging earthquake from the closest seismic source to the proposed area of the city. To verify the method and its computed results in Egypt, a study termed “method verification” was performed. I found that the October 12, 1992, earthquake (M b = 5.8) that occurred southwest of Cairo in the vicinity of the Dahshour region, at the coordinates 29.77°N, 31.07°E, is a significant earthquake to the city. The parameters of the path from the hypocenter of the event to the city were taken into consideration. To determine the site parameters, a shallow seismic refraction survey was carried out in the studied area. Accordingly, I simulated time-histories and pseudo-spectral accelerations from the October 12, 1992, earthquake at the location of seismic profiles. Finally, it is demonstrated that the site is characterized by high ground motion amplification factors, producing a high ground motion acceleration value.

11

Crustal structure of the Trans-European Suture Zone in Central Poland - reinterpretation of the LT-2, LT-4 and LT-5 deep seismic sounding profiles

Grad M., Guterch A., Polkowska-Purys A.

Geological Quarterly

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2005

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Vol. 49, No. 3

243--252

EN

The paper gives a reinterpretation of data from three deep seismic sounding profiles-LT-2, LT-4 and LT-5 - acquired in 1974-1979 between the Precambrian East European Craton (EEC) and the Palaeozoic Platform (PP) in Central Poland. Good quality seismic records in the distance interval from 50-90 to 200-280 km were the input data for the modelling of the crustal and uppermost mantle structure. Clear first arrivals and later phases of waves reflected/refracted from the crustal and the Moho boundaries were interpreted using a two-dimensional (2-D) ray tracing technique. In general, the crustal thickness along the three profiles varies from 30-35 km in the Palaeozoic platform area, to 42-44 km in the Polish part of the EEC, being 35-40 km in the transition zone between the PP and the EEC. In the transition area, the P-wave velocity is very low (Vp < 6.0 km/s) down to depths of 15-18 km, indicating that a very thick succession of sedimentary, metamorphosed or volcanic origin rocks is present there. All three 2-D models of the crust are discussed together with results obtained 20-30 years ago, particularly taking into account the difference in interpretation methods and new computation possibilities. Jointly with recent seismic studies along the profiles LT-7 and TTZ, as well as the POLONAISE'97 profiles P1-P4, the reinterpreted old profiles provide a collection of crustal models of the TESZ in Poland.

12

Integrated seismic refraction and geoelectric sounding inversion algorithm for systematic evaluation of aquifers

Sircar A.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 3

359-375

EN

This paper present an interesting idea of using seismic sounding data to stabilize the result of geoelectric sounding data. The seismic refraction data is inverted using a new inversion approach called Ray Inversion for Near Surface Estimation. The output of inversion is used to predict the initial guess for resistivity inversion through a database. The resistivity inversion is performed using a global optimization scheme called Evolutionary Programming. The efficacy of the integrated approach is demonstrated on synthetic and field data.