Numerical Simulation of Nonlinear Wave Propagation with Application to Geophysical Prospecting

Specifically, this research is intended to extend the use of the seismic reflection method to materials for which traditional linear wave analysis is insufficient

Artificial Neural Network in Seismic Reflection Method for Measuring Asphalt Pavement Thickness

A non‐destructive measurement of asphalt pavement layer thickness using seismic reflection was adopted together with coring test at similar site for comparison. The test was carried out on pavements around university campus’s road to measure the asphalt pavement layer thickness. The on-site seismic reflection testing was carried out using three piezoelectric sensors to capture time travel of wave motion, a light ball bearing to produce a high frequency seismic wave source and a data logger for data acquisition. The data processing is conducted in the time domain exclusively using a feedforward artificial neural network (ANN) using MATLAB software. A graphical interface is developed for viewing and extracting the result to make the processing of the seismic data feasible and user-friendly. The seismic reflection method analysis using the ANN successfully measured the asphalt pavement layer thickness. This study of the reflection method for measuring the pavement thickness compared with coring indicates the average accuracy of five testing sites was 93%. It shows that the seismic reflection able to demonstrate the capability to measure thickness of pavement in non-destructive way at a reliable accuracy

Ore-Body Delineation using Borehole Seismic Techniques for Hard Rock Exploration

Very often, economically viable ore deposits are low in volume and located at depth within extremely complex geological environments. Such deposits are difficult to explore. Borehole seismic methods, particularly crosshole reflection imaging, could be utilized to detect and delineate such resources. This study aims to evaluate the true potential of crosshole seismic reflection method for mineral exploration. One of the most promising applications of this method is in finding down-dip extensions of the existing resources

Common-reflection-surface imaging of shallow and ultrashallow reflectors

We analyzed the feasibility of the common-reflection-surface (CRS) stack for near-surface surveys as an alternative to the conventional common midpoint (CMP) stacking procedure. The data-driven, less user-interactive CRS method could be more cost efficient for shallow surveys, where the high sensitivity to velocity analysis makes data processing a critical step. We compared the results for two field data sets collected to image shallow and ultrashallow reflectors: an example of shallow Pwave reflection for targets in the first few hundred meters, and an example of SH-wave reflection for targets in the first 10 m. By processing the shallow P-wave records using the CMP method, we imaged several nearly horizontal reflectors with onsets from 60 to about 250 ms. The CRS stack produced a stacked section more suited for a subsurface interpretation, without any preliminary formal and time-consuming velocity analysis, because the imaged reflectors possessed greater coherency and lateral continuity. With CMP processing of the SHwave records, we imaged a dipping bedrock interface below four horizontal reflectors in unconsolidated, very low velocity sediments. The vertical and lateral resolution was very high, despite the very shallow depth: the image showed the pinchout of two layers at less than 10 m depth. The numerous traces used by the CRS stack improved the continuity of the shallowest reflector, but the deepest overburden reflectors appear unresolved, with not well-imaged pinchouts. Using the kinematic wavefield attributes determined for each stacking operation, we retrieved velocity fields fitting the stacking velocities we had estimated in the CMP processing. The use of CRS stack could be a significant step ahead to increase the acceptance of the seismic reflection method as a routine investigation method in shallow and ultrashallow seismics

New insights into the sedimentological-geophysical research of interlobate glaciofluvial complexes in western Finland

Interlobate eskers are the largest esker landforms in Finland. They formed in complex depositional conditions during the deglaciation of the Scandinavian ice sheet ca. 10 000 years ago. Their deposits can be 100 m thick, and they consist of high variety of sedimentary structures in large-scale depositional units. The significance of these large landforms to society is great as they host significant groundwater resources and sand and gravel deposits. In addition to protective legal procedures, thorough research and understanding of esker characteristics and groundwater conditions is vital for the sustainable use of eskers. The key to esker characterization is the use of a sedimentological approach for the recognition of the sedimentary structures and for the interpretation of the depositional conditions which formed the esker, as well as geophysical methods with adequate depth penetration. The combination of these two methods allows the characterization of large-scale architectural esker elements such as the coarse-grained esker core, overlapping esker fans and deformation structures (MUKHs) which form the basic hydrogeological units of the eskers. The reliable locating of these elements influencing the groundwater flow is essential in terms of groundwater utilization. In addition, knowledge on bedrock level and the variations in bedrock topography are needed to obtain the correct thickness of the esker deposits. The detailed sedimentological characterization of the Lohtaja-Kivijärvi esker revealed a new type of esker formed between two ice lobes, an ice-lobe margin esker. In the case of this esker, the interlobate environment was altered by the readvance of the neighboring ice lobe, and therefore this esker is not purely an interlobate esker. This esker challenges the assumption of thick and extensive eskers being formed between two ice lobes due to its modest extent and thickness. In addition, its depositional characteristics revealed changes in the ice dynamics as well as in the meltwater flow patterns. Researching thick interlobate esker deposits down to the bedrock level has not succeeded so far because the depth penetration of the available geophysical methods in Finland has not been adequate. The results of the first landstreamer-based high resolution seismic reflection pilot surveys in Finland on complex and thick interlobate esker deposits are represented. The results show the applicability of the landstreamer-based high-resolution seismic reflection method in the characterization of the interlobate esker architectural elements and bedrock level and topography variation. The combined use of the sedimentological approach and geophysical methods (ground penetrating radar and high-resolution seismic reflection) is recommended for the comprehensive understanding of thick and complex interlobate esker deposits and in the future potentially for large ice-marginal landforms like the Salpausselkäs.Saumaharjut ovat Suomen suurimpia harjumuodostumia. Ne syntyivät monimutkaisissa kerrostumisoloissa Skandinavian jäätikön sulamisvaiheen aikana noin 10 000 vuotta sitten. Niiden kerrostumat voivat olla 100 m paksuja, ja ne muodostuvat suuren mittakaavan kerrostumisyksiköistä ja niiden lukuisista erilaisista kerrostumisrakenteista. Näiden maaperämuodostumien merkitys yhteiskunnalle on huomattava niiden sisältämien pohjavesiresurssien sekä hiekka ja soravarojen vuoksi. Lisäksi niillä on geologista ja maisemallista arvoa. Lainsäädännöllisten toimien lisäksi harjujen ominaisuuksien ja pohjavesiolosuhteiden perusteellinen tutkimus ja ymmärrys ovat elintärkeitä harjujen kestävälle käytölle. Tämä voidaan saavuttaa harjujen suurten mittakaavan arkkitehtuuristen elementtien, kuten karkean harjuytimen, päällekkäisten harjuviuhkojen ja deformaatiorakenteiden (piilosupparakenteet), luonnehtimisella. Näiden pohjaveden virtauksen kannalta keskeisten rakenteiden luotettava paikantaminen on keskeistä pohjaveden hyödyntämisen kannalta. Lisäksi tarvitaan tietoa kalliopinnan tasosta ja vaihteluista kallionpinnan topografiassa, jotta harjukerrostumille saadaan oikea paksuus. Lohtaja-Kivijärvi-harjun yksityiskohtainen sedimentologinen luonnehdinta paljasti uuden tyyppisen, kahden jääkielekkeen välissä syntyneen harjun, jääloobin reunan harjun. Jääkielekkeiden välinen saumaympäristö oli muuttunut toisen jääkielekkeen uudelleenetenemisen myötä, ja siksi tämä harju ei ole puhtaasti saumaharju. Tämä harju haastaa pienen laajuutensa ja paksuutensa takia oletuksen siitä, että kahden jääkielekkeen väliin syntyvät harjut ovat paksuja ja laajoja. Lisäksi sen kerrostumisominaisuudet paljastivat muutoksia jäätikködynamiikassa sekä sulamisvesien virtauskuvioissa. Saumaharjujen jopa 100 metriä paksujen kerrostumien sisäisten rakenteiden tutkiminen kalliopintaan saakka ei ole onnistunut tähän mennessä, koska Suomessa saatavilla olevien soveltuvien geofysikaalisten menetelmien (maatutkan) syvyysulottuvuus ei ole siihen riittänyt. Tämä väitöskirjatyö esittelee Suomen ensimmäisen landstreamer-perusteisen tarkan resoluution heijastusseismisen pilottiluotauksen tulokset monimutkaisilta ja paksuilta saumaharjukerrostumilta. Tulokset osoittavat landstreameriin perustuvan tarkan resoluution heijastusseismisen menetelmän soveltuvuuden saumaharjujen arkkitehtuuristen elementtien sekä kallioperän tason ja topografian vaihtelun tarkasteluun. Sedimentologisen lähestymistavan ja geofysikaalisten menetelmien (maatutka ja tarkan resoluution heijastusseismiikka) yhteiskäyttöä suositellaan, jotta saavutetaan kokonaisvaltainen ymmärrys monimutkaisista saumaharjukerrostumista ja mahdollisesti tulevaisuudessa suurista reunamuodostumista, kuten Salpausselist

Identification of Source-Receiver Offset for the Presence of Air Wave

This paper presents the study of new method in finding hydrocarbon reservoirs which is Electromagnetic Sea Bed Logging (SBL ). This study will help to improve the effectiveness of SBL method in shallow water environment. SBL was introduced to overcome some limitations on the recent technology of finding the hydrocarbon reservoirs. Recent technology that is being used widely is seismic method via offset seismic technique which can help to estimate other characteristics of potential hydrocarbon reservoirs such as pore fluid and other rock properties. However, this method cannot distinguish the presence of hydrocarbon reservoir or gas-charged water (saline water) [1]. SBL can curb this problem since it detects the resistivity of the hydrocarbon which is relatively higher than saline water and sediments around it. However, at shallow water environment, this method will have some limitation due to the presence of the air waves. Air wave is the energy propagates from the source through the atmosphere to the receiver. Since air wave also have high resistivity, thus, it is hard to identify the presence of HC reservoir accurately. The study is started with some literature review first before going to do the simulation. Here, the author presents the literature review that had been done by him and the author also presents together data from Troll West gas Province offshore Norway which uses this method to detect the buried hydrocarbon reservoir. Other than that, the author also presents the methodology time line for his project on this topic

Seafloor Characterization Through the Application of AVO Analysis to Multibeam Sonar Data

In the seismic reflection method, it is well known that seismic amplitude varies with the offset between the seismic source and detector and that this variation is a key to the direct determination of lithology and pore fluid content of subsurface strata. Based on this fundamental property, amplitude-versus-offset (AVO) analysis has been used successfully in the oil industry for the exploration and characterization of subsurface reservoirs. Multibeam sonars acquire acoustic backscatter over a wide range of incidence angles and the variation of the backscatter with the angle of incidence is an intrinsic property of the seafloor. Building on this analogy, we have adapted an AVO-like approach for the analysis of acoustic backscatter from multibeam sonar data. The analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope (i.e. true incidence angle), time varying and angle varying gains, and area of insonification. Once the geometric and radiometric corrections are made, a series of “AVO attributes” (e.g. near, far, slope, gradient, fluid factor, product, etc.) are calculated from the stacking of consecutive time series over a spatial scale that approximates half of the swath width (both along track and across track). Based on these calculated AVO attributes and the inversion of a modified Williams, K. L. (2001) acoustic backscatter model, we estimate the acoustic impedance, the roughness, and consequently the grain size of the insonified area on the seafloor. The inversion process is facilitated through the use of a simple, interactive graphical interface. In the process of this inversion, the relative behavior of the model parameters is constrained by established inter-property relationships. The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, N.H., an area that we can easily access for ground-truth studies. AVO-derived impedance estimates are compared to in situ measurements of sound speed and AVO-derived grain-size estimates are compared to the direct measurement of grain size on grab samples. Both show a very good correlation indicating the potential of this approach for robust seafloor characterization

GEOLOŠKO-GEOFIZIČKA ISTRAŽIVANJA LEŽIŠTA BOKSITA PRIMJENA PLITKE SEIZMIČKE REFLEKSIJE

The exploration of bauxite deposits in the region of the carbonaceous Dinarides has been performed by using different geological and geophysical methods. Deposits laying shallower or deeper below the roof sediments have so far most often been discovered by expensive drilling methods in a corresponding grid. Complex geological explorations have led to a series of valuable data thus enabling the application of other much more economical methods as well. In the region of the bauxite sedimentary basin Mesihovina-Rakitno, western Herzegovina, at the site of Studena vrila - after extensive geological explorations - a conclusion was drawn that the shallow seismic reflection geophysical method as well might be successfully applied in locating new bauxite deposits. In the paper, the geological framework of the bauxite deposits occurrences, stipulating the selection of this methode, will be presented. Measurements were performed on a known deposit (L-84, Povaljenica), completely defined by exploration drilling. The obtained results justify the selection of the shallow seismic reflection method as one of the methods for exploring bauxite deposits beneath the roof beds.Istraživanje ležišta boksita, u području karbonatnih Dinarida. obavlja se uz pomoć različitih geoloških i geofizičkih metoda. Ležišta pliće ili dublje ispod krovinskih sedimenata do sada su najčešće pronalažena skupim metodama bušenja u odgovarajućoj mreži. Kompleksnim geološkim istraživanjima došlo se do niza vrijednih podataka koji omogućuju primjenu i drugih ekonomičnijih metoda. U području boksitonosnog sedimentacijskog bazena Mesihovina - Rakitno. zapadna Hercegovina, na lokalitetu Studena vrila nakon obimnih geoloških istraživanja došlo se do spoznaje da bi se pri pronalaženju novih ležišta boksita mogla s dosta uspjeha koristiti i geofizička metoda plitke seizmičke refleksije. U radu su izloženi geološki okviri pojavljivanja ležišta boksita koji su uvjetovali odabir ove metode. Mjerenja su izvedena na poznatom ležištu (L-84, Povaljenica) koje je u potpunosti definirano istražnim bušenjem. Dobiveni rezultati opravdavaju izbor plitke seizmičke refleksije kao jedne od metoda kod istraživanja ležišta boksita ispod krovinskih naslaga