An integrated geophysical study was conducted to investigate the subsurface regional structure and the presence of a Quaternary sedimentary basin in the Olak Lempit - Banting area of Selangor, Malaysia. A regional gravity survey and the high resolution reflection seismic were employed to determine the thickness and areal distribution of the alluvial sedimentary basin as well as to investigate the depth and topography of the bedrock in the study area. The sedimentary basin hosts one of the most important coastal alluvial aquifer which was used to cater the shortage of domestic water supply during the worst water crisis that hit the state of Selangor in 1998. The surface geological map shows that in general 70% of the study area is covered by Quaternary deposits of Beruas, Gula and Simpang Formations which overlie the sedimentary bedrock of Kenny Hill Formation. The Beruas Formation consists of mainly clay, sandy clay and peat of Holocene fluviatile-estuarine deposits, whereas the Gula Formation represents Holocene marine to estuarine sediments which mostly consists of clay and minor sand. The Simpang Formation (Pleistocene) is a continental deposit comprising of gravel, sand, clay and silt. The underlying Kenny Hill Formation consists of a monotonous sequence of interbedded shales, mudstones and sandstones. The rock is Carbonaceous in age and it forms an undulating surface topography in the eastern part of the study area. A total of 121 gravity stations were established using a La Coste & Romberg gravity meter and the elevations of most of the stations were determined barometrically using Tiernan-Wallace altimeters. The high resolution seismic reflection using the common mid point (CMP) or roll along technique was carried out using a 24 channel signal enhancement seismograph and high frequency geophones. A total length of about 1.7 km stacked seismic section has been acquired in this survey and a nearby borehole data was used for interpretation. A relative Bouguer anomaly map shows an elongated zone of low gravity anomaly trending approximately NW-SE which is interpreted to be the deposition center of the Quaternary basin. The interpreted gravity profiles running across the central area of the study area show that the basin has thickness varies from tenth to several hundred meters with maximum depth to bedrock of about 275m. A gravity profile which passes through the eastern edge of the basin was modeled with depth to bedrock of about 178m below ground which agrees very well with those obtained from the interpreted seicmic section and borehole data. The stacked seismic section shows several high amplitude parallel to sub-parallel reflection overlying discontinuos and low reflection pattern. Reflections on the eastern part of the section is much shallower than the one observed on the western part which clearly indicates the presence of basinal structure with a total interpreted depth to bedrock of about 200 meters.
Magnetic surveys were carried out in Farigh area which is located in the eastern part of the Libyan Sirte basin. Interpretation of the onshore magnetic anomaly of this area, suggests that the high total magnetization may be caused by an intrusive body. Analysis of the magnetic power spectra indicates the presence of four sub-anomalies at depths of 340 m, 1400 m, and 2525 m which is probably related to the igneous rocks. The presence of igneous rock as basement at depth of 4740 m was confirmed by drilling. Assuming that all rock magnetization in the area is caused by induction in the present geomagnetic field, it strongly suggests that the causative structure has a remnant magnetization of declination (D) = −16° and inclination (I) = 23°. Based on pseudogravity data, the total horizontal derivative map shows high gradient values in NW-SW trends related to the structures in the eastern part of the Sirte basin. The 3D Euler deconvolution map derived from gravity data clearly indicates the location of igneous body in the study area as well as its tectonic trends and depth, which is estimated at 350 m to 1400 m below the surface. Depth of gravity anomalies at 1400 m to 2525 m is considered as anomalies in between shallow and deep. Anomaly at depth of approximately 4740 m below the surface is interpreted as basement rock. Geologically, the magnetic survey shows that the source of anomaly is a mafic igneous rock of Early Cretaceous age. The study also discovered a left-lateral sheared fault zone along the NW-SE of Hercynian age which was believed to be reactivated during Early Cretaceous.
Analisis kimia air telah dilakukan terhadap larutan yang diekstrak dari 85 sampel tanah yang dipungut di kawasan ternakan udang harimau di Kerpan. Sampel tanah dikorek pada kedalaman 2 m bermula dari garis pantai sehingga 20 km ke arah daratan. Selain daripada tanah, air bawah tanah juga disampel dengan penggerudian yang berkedalaman 10 hingga 25 m untuk dilakukan analisis kimia air. Hasil analisis hidrokimia larutan yang diekstrasi dari sampel tanah yang diambil pada kedalaman 1-2 m menunjukkan kepekatan klorida berjulat dari 12 hingga 6500 mg/L. Berdasarkan kepekatan ion tersebut, kawasan kajian telah dibahagikan kepada beberapa zon-zon iaitu zon masin dan payau. Kepekatan pepejal terlarut yang diukur adalah dalam julat 100 hingga 40,000 mg/L dengan julat ini merangkumi zon berair segar hingga masin. Zon berair masin yang ditafsir berdasarkan kepekatan pepejal terlarut adalah dalam lingkungan 1 km dari pantai manakala berdasarkan kepekatan klorida sempadan ini adalah disekitar 4-5 km. Kehadiran air masin boleh berasal dari penerobosan langsung dari laut ataupun melalui proses air pasang-surut dimana air laut masuk melalui sungai atau terusan berhampiran ke kawasan kajian. Kehadiran air masin juga disokong oleh pertambahan kepekatan unsur-unsur seperti naterium, kalium dan kalsium ke arah laut. Berdasarkan peta taburan spatial kepekatan klorida, pola kontur kemasinan tinggi didapati mengikut bentuk kolam ternakan udang. Oleh itu besar kemungkinan pengaruh air masin adalah dari proses infiltrasi air kolam ke kawasan sekitar. Untuk melihat samada proses penerobosan juga turut memainkan peranan dalam mempengaruhi kemasinan di kawasan kajian, sampel air dari lubang gerudi pada kedalaman 10-25 meter juga turut dibuat. Sampel air yang dipam dari lubang gerudi menunjukkan kepekatan klorida dalam julat 2030 hingga 13,000 mg/L manakala kepekatan pepejal terlarut berjulat 3233 hingga 9280 mg/L. Berdasarkan nilai kepekatan klorida dan pepejal terlarut sampel air lubang gerudi, kawasan di sekitar lubang gerudi khususnya pada jarak hampir 1 km dari pantai telah tercemar dengan kesan penerobosan air laut.
Geophysical surveys in particular Ground Penetrating Radar (GPR), geoelectrical Resistivity Tomography (ERT) and Vertical Resistivity Probe (VRP) were used in mapping the subsurface geological structures and groundwater contaminants at Sungai Kandis, Klang to identify the approximate boundaries of contaminant plumes and to provide stratigraphic information at this site. The study area was formerly an illegal dumping site of hydrocarbon and toxic waste. A good correlation exists between GPR signatures, ERT layers, vertical resistivity probe and the contaminated soil. The presence of contaminant plumes as well as the water table are also observed in the GPR and ERT sections at depths approximately of 0.5 to 1 m. In this study, a total of 16 GPR traverses and 10 ERT lines with lengths from 30 to 100 m were established. VRP measurements were conducted in 14 shallow boreholes with a maximum depth of about 1 m. The VRP results show high apparent resistivity values ranging from 200 to 10000 Ωm associated with an oil contaminated layer. The presence of this layer was also detected in the 2D resistivity sections as a thin band of high resistivity values ranging from 60 to 200 Ωm. In the GPR section, the oil contaminated layer exhibits discontinuous, subparallel and chaotic high amplitude reflection patterns.
A geotechnical study needs to be carried out to determine the engineering parameters of the rock mass at the project site in executing construction projects such as tunnels, dams, highways and buildings. Design and safety factor of the construction are highly dependent on soil and rock engineering parameters which are usually determined by in-situ test such as Standard Penetration Test (SPT) and seismic tests. The SPT test which normally involves drilling and laboratory works always incur high operating cost, while seismic tests on the other hand are fast, cheap, non-destructive and an easy to operate method for rock mass characterization. The spectral analysis of surface waves (SASW) method is an in situ and non-destructive measurement that is rapid and cost effective. The aims of this study were to determine Rock Quality Designation (RQD) value, excavation classification analysis as well as site characterization by using the SASW method. WinSASW 3.1.3 was used for inversion processing of the SASW data to produce shear wave velocity (Vs) versus depth profiles. The profiles were then analyzed and correlated with rock mass engineering geological parameters such as RQD and site characterization as well as excavation classification of rock mass. Twenty (20) SASW tests were conducted on the granitic rock mass and four (4) SASW tests were conducted on a cut hill slope of metasedimentary rocks. RQD values were computed based on shear wave velocities and ultrasonic velocities of intact (fresh) rock. The differences between RQD obtained from SASW method and those from discontinuity survey were found to be less than 10%. Excavation classification for granitic rock mass at JKR Quarry was empirically determined using both SASW and ultrasonic velocities as well as RQD value of the rock mass. Site characterization for metasedimentary rocks mass at Bukit Tampoi was determined based on shear wave velocities from SASW method.
An integrated geoelectrical and geochemical techniques were used to investigate and delineate different types of groundwater in Kuala Selangor-Batang Berjuntai alluvial aquifer. Previous hydrogeological borehole investigations showed that this aquifer contained several types of groundwater in relation to its salinity. The high salinity of the groundwater in some areas was believed to be due to either saltwater intrusion from the nearby sea or river infiltration during tide season. Both vertical electrical sounding (VES) and 2-D electrical resistivity imaging methods were employed to study and map the subsurface variation of resistivity in the area. For each measurement, a total spread length of 200 m was obtained with vertical depth penetration of about 60 to 100 m. Chemical analysis data of the groundwater samples taken from both shallow and deep boreholes were used in the interpretation of the groundwater interfaces. A total of 45 VES stations were succesfully established along three parallel roads with direction almost perpendicular to the coastal line. The distance between stations vary from 1 - 2 km with a maximum length of about 60 km surveyed line. Results of the vertical electrical soundings and resistivity imaging as well as the chemistry of the groundwater samples showed that groundwater in the study area can be grouped into three types i.e. fresh water (resistivity >100 Ωm.), brackish water (5-100 Ωm.) and salt water (resisitvity <5 Ωm.). The subsurface resistivity sections derived from the VES study suggest that the boundary between fresh and salt water was located between 4 to 8 km from the present coastal line. This result appears to agree well with the groundwater interfaces obtained from the chloride concentration map. Values greater than 300 ppm was considered to be representing zone of brackish water whilst values greater than 800 ppm represents saline water zones.
A 2D electrical resistivity survey was conducted to investigate the subsurface contamination underneath a domestic waste disposal site at Ampar Tenang, Dengkil, Selangor. The resistivity imaging technique was used in this study to locate the vertical and horizontal extend of contamination plumes underneath the site. A total of six 2-D resistivity imaging lines were established with two of them located outside the landfill area while one of them located in inactive landfill site. Another three lines were situated in the active landfill site. The results of the survey show that the resistivity value of the decomposed waste material in the inactive site of landfill is relatively low and the contaminated leachate plumes has low resistivity value of less than 2 Ωm. Characterisation of subsurface resisitivity and its relation to lithology was interpreted based on the available borehole data.
Survei keberintangan geoelektrik ini telah dijalankan di kawasan Bukit Tenggek, Setiu, Terengganu untuk mengesan kemungkinan wujudnya terowong lama yang dipercayai berada di kawasan berkenaan. Kaedah keberintangan geoelektrik ini bukanlah asing dan didapati amat berkesan di dalam eksplorasi mencari bahan arkeologi dan struktur terkambus di bawah tanah (terowong dan bahan artifak). Survei keberintangan geoelektrik ini dijalankan dengan menggunakan peralatan ABEM Terrameter SAS1000 dan susun atur elektrod jenis Wenner. Kawasan kajian terletak di kawasan lembah yang lembap dan terdapat anak sungai yang merentasi kawasan tersebut. Imej keberintangan 2-D menunjukkan wujudnya beberapa kawasan beranomali yang boleh dikaitkan dengan struktur yang dicari. Nilai keberintangan yang rendah mewakili kawasan yang dianggarkan wujudnya terowong lama. Manakala anomali yang menunjukkan bentuk gugusan dianggarkan berasosiasi dengan lokasi tong/bahan artifak. Profil keberintangan 3-D menunjukkan anomali yang mungkin disebabkan oleh wujudnya satu terowong mendatar dan dua terowong menegak. Namun, kerja galicari perlu dilakukan bagi menentukan punca sebenar anomali tersebut.
Lembangan Tuba adalah satu endapan aluvium yang terletak di antara perbukitan granit di bahagian barat Pulau Tuba dan tanah tinggi batuan sedimen Formasi Setul di bahagian barat. Lembangan ini menganjur timur laut ke arah barat daya sepanjang hampir 3 km dan mempunyai kelebaran sejauh 2 km. Satu survei geofizik permukaan menggunakan teknik geoelektrik telah dilakukan untuk mengkaji struktur subpermukaan dan mengesan kehadiran sebarang akuifer serta jenis nya dalam lembangan ini. Di samping itu, kepekatan unsur-unsur dalam air tanah juga dianalisis untuk melihat kebarangkalian berlakunya intrusi air laut ke dalam akuifer pantai. Sebanyak 22 stesen telah dipilih secara rawak di
seluruh kawasan kajian untuk dilakukan survei geoelektrik duga-dalam. Sementara itu air bawah tanah telah diambil dari 11 telaga untuk analisis kimia di makmal. Hasil analisis mendapati semua sampel air perigi ini adalah berjenis air tawar. Profil keberintangan pada arah timur laut - barat daya yang menganjur dari Teluk Berembang hingga Teluk Bujur mempunyai nilai keberintangan yang berkisar di antara 4 Ωm sehingga infiniti. Lapisan teratas yang mempunyai ketebalan sekitar 1-3 meter dan berkeberintangan 4 -12 Ωm ditafsirkan sebagai lempung manakala lapisan di bawahnya
yang berketebalan 10 hingga 50 meter dengan nilai keberintangan 2 - 480 Ωm ditafsirkan sebagai bahan berpasir dengan air tawar atau pasir berair payau. Keberintangan berjulat ribuan ohm.m hingga infiniti dianggap mewakili batuan dasar granit dan batu kapur. Kedalaman maksimum yang dicapai oleh survei keberintangan ialah sekitar 70 m.
An archeological study, conducted by the Archaeological Global Research Centre, Universiti Sains Malaysia shows the evidence of shock metamorphisms (suevite breccia) and crater morphology at Bukit Bunuh in Lenggong area of north Perak, Malaysia. A regional gravity survey focusing at Bukit Bunuh and its surrounding area was conducted to justify the occurrence and to determine the diameter and subsurface geological structure of the Bukit Bunuh impact crater. The gravity survey, using a Scintrex CG5 gravity meter, comprises 476 gravity stations with a 500 m spacing covering an area of approximately 160 km2. The elevation of the gravity stations were obtained by using a pair of Wellace and Tiernan altimeters. The gravity data were corrected for drift, free air, bouguer, latitude and terrain in order to produce a corrected gravity data of the study area. The data were processed and analysed using Oasis Montaj (Geosoft software) to produce bouguer, residual, Total Horizontal Derivative (THD) residual, regional and Total Horizontal Derivative (THD) regional anomaly maps for qualitative and quantitative interpretations. The bouguer gravity map shows relatively low negative anomaly with nearly circular shaped contour around the Bukit Bunuh area. This anomaly was interpreted as the remnant of meteorite impact structure with rounded shaped crater in the study area. The bouguer anomaly map shows that the Bukit Bunuh impact crater has a diameter of approximately 2.5 km. The impact structure was successfully modeled as a complex impact crater with maximum depth of about 300 m. The bouguer anomaly map also showed the possible occurences of at least two more impact craters located in the northeast and southeast areas of the Bukit Bunuh crater and these structures need further investigation for confirmation.