Seismic Data Interpretation

This paper describes some results of the research undertaken over the Brown Bank area during recent (2018/2019) geoarchaeological surveys in the North Sea which included seismic imaging, shallow (vibro)coring and dredging. It examines the benefits of simultaneous high-resolution (0.5 – 1 m) and ultra-high-resolution (10–20 cm) seismic survey techniques and a staged approach to resolving the submerged Holocene landscape in the highest possible detail for the purpose of targeted prospecting for archaeological material from the Mesolithic landscape of Doggerland. The materials recovered from such surveys offer significantly greater information due to an enhanced understanding of the context in which they were recovered. The importance of this information cannot be understated archaeologically, as few locations on land provide the opportunity to recover archaeological finds in situ within preserved landscapes. Moreover, it allows offshore areas of potential human activity to be prospected with some certainty of success.

To remove some of the ambiguities in a heterogeneous oil reservoir, a three dimensional model of the reservoir would be constructed by application of newly introduced methods. The aim of this study is to define an accurate and efficient model of a complex reservoir in southwest of Iran and accurately derive the geological and geometrical properties of the reservoir for well location proposal. Seismic data in addition to well logs were used for that purpose. A corner point grid was used in this study, and a generic global scale-up method was combined with previous result for reservoir simulation. The final model pointed out the heterogeneous characterization of the reservoir and proved the advantage of combining these methods in constructing accurate and efficient reservoir models. According to these models, it is concluded that the reservoir has different productive zones in different members that was not cleared in the previous models.

During the past decade, the size of 3D seismic data volumes and the number of seismic attributes have increased
to the extent that it is difficult, if not impossible, for interpreters to examine every seismic line and time slice. To address this problem, several seismic facies classification algorithms including k-means, self-organizing maps, generative topographic mapping, support vector machines, Gaussian mixture models, and artificial neural networks have been successfully used to extract features of geologic interest from multiple volumes. Although well documented in the literature, the terminology and complexity of these algorithms may bewilder the average seismic interpreter, and few papers have applied these competing methods to the same data volume. We have reviewed six commonly used algorithms and applied them to a single 3D seismic data volume acquired over the
Canterbury Basin, offshore New Zealand, where one of the main objectives was to differentiate the architectural
elements of a turbidite system. Not surprisingly, the most important parameter in this analysis was the choice of
the correct input attributes, which in turn depended on careful pattern recognition by the interpreter. We found
that supervised learning methods provided accurate estimates of the desired seismic facies, whereas unsupervised
learning methods also highlighted features that might otherwise be overlooked.

(In English) The strong and felt earthquake with magnitude 6.5 occurred in 119 km to the southeast of Cilacap Regency, Central Java Province at a depth of 48 km. The earthquake centered on the sea at coordinates 8.48o latitude and 109.17o east longitude on January 25, 2014. The earthquake triggered damage in several locations, including the districts of Banyumas, Kebumen, Cilacap and Purworejo. In order to mitigate natural hazards, this study aims to determine the relationship between seismic wave velocity and depth of layers near the surface in shallow geological structures. The method used in this study is the seismic refraction method. This method is done by interpreting seismic signals from man-made waves that spread near the surface of the earth. The seismogram will display the travel time of the waves, the distance between the waves and the source of the waves themselves. The structure of the geological layers that exist in the earth can be estimated based on the magnitude of the seismic wave velocity. This research is located in the campus area of the Indonesian Institute of Sciences Karangsambung. Measurements were made considering its location close to the center of the earthquake and the uniqueness of the rock formed by the removal of the ocean floor. Based on the results of the study it is known that there is a relationship between seismic wave velocity and the depth of the layers near the surface. The deeper the layer of soil from the earth's surface, the seismic wave velocity will be higher.

Keywords: seismic; refraction; geo-hazard; soil property

(In Bahasa) Gempabumi kuat dan dirasakan dengan kekuatan magnitudo 6.5 terjadi di 119 km ke arah tenggara Kabupaten Cilacap, Propinsi Jawa Tengah pada kedalaman 48 km. Gempabumi tersebut berpusat di laut pada koordinat 8.48 o LS dan 109.17 o BT pada tanggal 25 Januari 2014. Gempabumi tersebut memicu dampak kerusakan di beberapa lokasi, termasuk kabupaten Banyumas, Kebumen, Cilacap dan Purworejo. Dalam rangka mitigasi bahaya alam kebumian, maka penelitian ini bertujuan untuk mengetahui hubungan antara kecepatan gelombang seismik dengan kedalaman lapisan-lapisan dekat permukaan pada struktur geologi dangkal. Metode yang digunakan dalam penelitian ini adalah metode seismik refraksi. Metode ini dilakukan dengan menginterpretasi sinyal seismik dari gelombang buatan manusia yang menjalar di dekat permukaan bumi. Seismogram akan menampilkan waktu tempuh gelombang, jarak antar gelombang dan sumber gelombangnya sendiri. Struktur lapisan geologi yang ada di dalam bumi dapat diperkirakan berdasarkan besarnya kecepatan gelombang seismik. Penelitian ini berlokasi di area kampus Lembaga Ilmu Pengetahuan Indonesia (LIPI) Karangsambung. Pengukuran dilakukan mengingat lokasinya yang dekat dengan pusat gempabumi dan keunikan batuannya yang terbentuk dari pengangkatan lantai dasar samudra. Berdasarkah hasil penelitian diketahui bahwa terdapat hubungan antara kecepatan gelombang seismik dengan kedalaman lapisan-lapisan dekat permukaan. Semakin dalam lapisan tanah dari permukaan bumi, maka kecepatan gelombang seismik akan semakin tinggi.

Kata kunci: seismik refraksi, bahaya kebumian, sifat tanah

The northern Gulf of Elat/Aqaba is located in the transition between the deep marine basins of
the gulf and the shallow onland basins of the Arava Valley. Interpretation of 500 km of high-resolution seismic
reflection data collected across the northern shelf reveals the tectonic structure and evolution of this
transition. Six NNE-trending faults and one E-W trending transverse fault are mapped. Slip rates are calculated
based on measured offsets and age determination based on a radiocarbon-calibrated sedimentation rate and
a Quaternary age model. The most active fault is the Evrona Fault that absorbs most of the left lateral slip
within the basin with an average sinistral slip rate of 0.7 ± 0.3 mm/yr through the Late Pleistocene and
2.3–3.4 mm/yr during the Holocene. Two intrabasin faults east of the Evrona Fault that have been inactive for
the last several tens of thousands of years were mapped, and motion from these faults has likely transferred
to the Evrona Fault. The basin is flanked on the west by the Elat Fault and on the east by the Aqaba Fault. Both
faults are marked by large bathymetric escarpments. Based on displaced seismic reflectors, we calculate a
Holocene vertical slip rate of 1.0 ± 0.2 and 0.4 ± 0.1 mm/yr for the Elat and Aqaba Faults, respectively. The
geometry, slip rates, and slip history of the northern Gulf of Elat/Aqaba faults show that during the Late
Pleistocene several intrabasin faults became dominant across the basin but that during the Holocene the
Evrona Fault accommodates most of the strike slip.

In a high-resolution small scale seismic experiment we investigated the shallow structure of the Wadi Araba Fault (WAF), the principal fault strand of the Dead Sea Transform System between the Gulf of Aqaba/Eilat and the Dead Sea. The experiment consisted of 8 sub-parallel 1 km long seismic lines crossing the WAF. The recording station spacing was 5 meters and the source point distance was 20 m. The first break tomography yields insight into the fault structure down to a depth of about 200 m. The velocity structure varies from one section to the other which were 1 to 2 km apart, but distinct velocity variations along the fault are visible between several profiles. The reflection seismic images show positive flower structures and indications for different sedimentary layers at the two sides of the main fault. Often the superficial sedimentary layers are bent upward close to the WAF. Our results indicate that this section of the fault (at shallow depths) is characterized by a transpressional regime. We detected a 100 to 300 m wide heterogeneous zone of deformed and displaced material which, however, is not characterized by low seismic velocities at a larger scale. At greater depth the geophysical images indicate a blocked cross-fault structure. The structure revealed, fault cores not wider than 10 m, are consistent with scaling from wear mechanics and with the low loading to healing ratio anticipated for the fault.

L’analyse de plusieurs profils sismiques calibrés aux données de puits et de terrain, ainsi que la cartographie isochrone et
isopaque des horizons jurassiques enfouis sous l’Atlas révèlent une structuration différenciée dès le Jurassique moyen associée,
d’une part, au jeu d’un réseau de failles de directions NE–SW, nord–sud, est–ouest, NW–SE et, d’autre part, à la montée des
évaporites du Trias supérieur, qui s’est effectuée préférentiellement par intrusion le long de ces failles. Les intumescences triasiques,
sous forme de coussins de sels ou de dômes, sont observées au voisinage de la faille nord–sud de Sidi Ali Ben Aoun
et des ramifications N60 de Sidi Aïch et N120 de Majoura, engendrant des gouttières subsidentes bordées par des domaines de
plates-formes résistantes. La migration précoce des évaporites, qui semble être associée à la fracturation de la plate-forme carbonatée
initiale (Lias inférieur), lors du rifting liasique, est attestée par de grandes variations d’épaisseur, la présence de biseaux
stratigraphiques en onlap d’aggradation et de rétrogradation, au Jurassique moyen, entre les zones de gouttières en rim-synclines
et les zones de plates-formes. Ces mouvements halocinétiques sont aussi perceptibles par les migrations de gouttières de dépôtscentres
du Jurassique moyen et du Jurassique supérieur. Autour de la région de Majoura–El Hfay, le mouvement ascendant du
Trias s’est poursuivi au Crétacé et au Tertiaire, engendrant ainsi des diapirs perçants.

The Chatham Rise is located offshore of New Zealand’s South Island. Vast areas of the Chatham Rise are covered in circular to elliptical seafloor depressions that appear to be linked to bathymetry. Seafloor depressions 2-5 km in diameter are found in a water depths of 800-1100 m. High resolution P-Cable 3D seismic data were acquired in 2013 across one of the these depressions. The seafloor depression is interpreted as a mounded contourite. Our data reveal several smaller buried depressions (<20-650 m diameter) beneath the mounded contourite that we interpret as paleo-pockmarks. These pockmarks are underlain by a complex polygonal fault system that deforms strata and an unusual conical feature. We interpret the conical feature as a sediment remobilization structure based on the presence of stratified reflections within the feature, RMS amplitude values and lack of velocity anomaly that would indicate a non-sedimentary origin. The sediment remobilization structure, polygonal faults and paleo-depressions are indicators of past subsurface fluid flow. We hypothesize that the pockmarks provided the necessary topographic roughness for formation of the mounded contourites thus linking fluid expulsion and deposition of contouritic drifts.