Regional Tectonics & Structural Framework of Offshore Aceh's Andaman Sub-Basin, Northern Sumatra, Indonesia

2021 ◽  
Author(s):  
S. Clark
Keyword(s):  
High Resolution ◽  
Late Eocene ◽  
Strike Slip ◽  
Hydrocarbon Exploration ◽  
Fault System ◽  
Earth Model ◽  
The West ◽  
Structural Framework ◽  
Geochemical Models ◽  
Regional Tectonics

The three-way collision of the Indo-Australian, Eurasian and Pacific plates have resulted in Southeast Asia being the most tectonically complex region on Earth. This is particularly true for Offshore Aceh’s Andaman Sub-Basin, which has undergone complex late Eocene-Recent evolution. Despite a long history of hydrocarbon exploration and production, data scarcity in the offshore means that the Sub-Basin’s regional tectonics and structural framework have been poorly understood. Pre-1996 2D seismic data were low-fold and low-offset, however the 2019 PGS (NSMC3D) regional 3D survey imaged the entire Cenozoic sequence, enabling the delineation of a high-resolution tectonic framework for the first time. Integration of interpretations drawn from geophysical datasets with a 2019 biostratigraphy study has refined the ages of critical sequence boundaries and advanced the understanding of major structural elements. GEM™, the Geognostics Earth Model, has been used to place these interpretations in a regional tectonic and kinematic context using a series of high resolution plate animations. Andaman Sub-Basin formation initiated in response to the northward motion of India and collision with Eurasia, suturing the West Burma and Sibumasu Terranes through the middle-late Eocene. Continued northward motion of the Indo-Australian Plate resulted in further subduction along the Sunda Trench with associated oblique back-arc extension in present-day onshore and offshore Java and Sumatra. Concurrent rotation of Sundaland, with sinistral strike-slip motion along the Ranong and Khlong Mauri fault zones, resulted in the two rifting phases within the late Eocene (~40Ma) to early Oligocene in the Andaman Sub-Basin. Significant inversion events at 30Ma and 23Ma formed in response to dextral transpression associated with rotational extrusion of Indochina and Sundaland. Rapid subsidence followed the 30Ma inversion, resulting in a switch to post-rift sag and bathyal conditions during which turbidites infilled seabed topography. The onset of dextral strike slip between the West Burma Terrane along the Saigang fault system occurred at ~26Ma, causing transtension in the Andaman Sub-basin that terminated at 23Ma. At approximately 5Ma inversion and toe thrusts developed along the Sub-Basin’s southern margin due to uplift within the Barisan mountains. Refinement of the tectonic model, integrated with updated biostratigraphic and geochemical models, resulted in a revised tectono-stratigraphy for the Andaman Sub-Basin, which provides a predictive depositional model in which paleogeography and structural reactivation can be understood in a regional context.

CONTINENTAL SHELF BASINS ON THE WEST TASMANIA MARGIN

1992 ◽  
Vol 32 (1) ◽  
pp. 231 ◽  
Author(s):  
A.M.G. Moore ◽  
J.B. Willcox ◽  
N.F. Exon ◽  
G.W. O'Brien
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Late Cretaceous ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Strike Slip ◽  
Source Rocks ◽  
Fault System ◽  
The West ◽  
Shallow Marine

The continental margin of western Tasmania is underlain by the southern Otway Basin and the Sorell Basin. The latter lies mainly under the continental slope, but it includes four sub-basins (the King Island, Sandy Cape, Strahan and Port Davey sub-basins) underlying the continental shelf. In general, these depocentres are interpreted to have formed at the 'relieving bends' of a major left-lateral strike-slip fault system, associated with 'southern margin' extension and breakup (seafloor spreading). The sedimentary fill could have commenced in the Jurassic; however, the southernmost sub-basins (Strahan and Port Davey) may be Late Cretaceous and Paleocene, respectively.Maximum sediment thickness is about 4300 m in the southern Otway Basin, 3600 m in the King Island Sub-basin, 5100 m in the Sandy Cape Basin, 6500 m in the Strahan Sub-basin, and 3000 m in the Port Davey Sub-basin. Megasequences in the shelf basins are similar to those in the Otway Basin, and are generally separated by unconformities. There are Lower Cretaceous non-marine conglomerates, sandstones and mudstones, which probably include the undated red beds recovered in two wells, and Upper Cretaceous shallow marine to non-marine conglomerates, sandstones and mudstones. The Cainozoic sequence often commences with a basal conglomerate, and includes Paleocene to Lower Eocene shallow marine sandstones, mudstones and marl, Eocene shallow marine limestones, marls and sandstones, and Oligocene and younger shallow marine marls and limestones.The presence of active source rocks has been demonstrated by the occurrence of free oil near TD in the Cape Sorell-1 well (Strahan Sub-basin), and thermogenic gas from surficial sediments recovered from the upper continental slope and the Sandy Cape Sub-basin. Geohistory maturation modelling of wells and source rock 'kitchens' has shown that the best locations for liquid hydrocarbon entrapment in the southern Otway Basin are in structural positions marginward of the Prawn-1 well location. In such positions, basal Lower Cretaceous source rocks could charge overlying Pretty Hill Sandstone reservoirs. In the King Island Sub-Basin, the sediments encountered by the Clam-1 well are thermally immature, though hydrocarbons generated from within mature Lower Cretaceous rocks in adjacent depocentres could charge traps, providing that suitable migration pathways are present. Whilst no wells have been drilled in the Sandy Cape Sub-basin, basal Cretaceous potential source rocks are considered to have entered the oil window in the early Late Cretaceous, and are now capable of generating gas/condensate. Upper Cretaceous rocks appear to have entered the oil window in the Paleocene. In the Strahan Sub-Basin, mature Cretaceous sediments in the depocentres are available to traps, though considerable migration distances would be required.It is concluded that the west Tasmania margin, which has five strike-slip related depocentres and the potential to have generated and entrapped hydrocarbons, is worthy of further consideration by the exploration industry. The more prospective areas are the southern Otway Basin, and the Sandy Cape and Strahan sub-basins of the Sorell Basin.

scholarly journals Active fault segments along the North Anatolian Fault system in the Sea of Marmara: implication for seismic hazard

2021 ◽  
Author(s):  
Luca Gasperini ◽  
Massimiliano Stucchi ◽  
Vincenzo Cedro ◽  
Mustapha Meghraoui ◽  
Gulsen Ucarkus ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Hazard ◽  
Seismic Reflection ◽  
Strike Slip ◽  
North Anatolian Fault ◽  
Sediment Supply ◽  
Fault System ◽  
Sea Of Marmara ◽  
Seismic Reflection Data ◽  
The North

AbstractA new analysis of high-resolution multibeam and seismic reflection data, collected during several oceanographic expeditions starting from 1999, allowed us to compile an updated morphotectonic map of the North Anatolian Fault below the Sea of Marmara. We reconstructed kinematics and geometries of individual fault segments, active at the time scale of 10 ka, an interval which includes several earthquake cycles, taking as stratigraphic marker the base of the latest marine transgression. Given the high deformation rates relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor, even in presence of composite fault geometries and/or overprinting due to mass-wasting or turbidite deposits. In the frame of the right-lateral strike-slip domain characterizing the North Anatolian fault system, three types of deformation are observed: almost pure strike-slip faults, oriented mainly E–W; NE/SW-aligned axes of transpressive structures; NW/SE-oriented trans-tensional depressions. Fault segmentation occurs at different scales, but main segments develop along three major right-lateral oversteps, which delimit main fault branches, from east to west: (i) the transtensive Cinarcik segment; (ii) the Central (East and West) segments; and (iii) the westernmost Tekirdag segment. A quantitative morphometric analysis of the shallow deformation patterns observed by seafloor morphology maps and high-resolution seismic reflection profiles along the entire basin allowed to determine nature and cumulative lengths of individual fault segments. These data were used as inputs for empirical relationships, to estimate maximum expected Moment Magnitudes, obtaining values in the range of 6.8–7.4 for the Central, and 6.9–7.1 for the Cinarcik and Tekirdag segments, respectively. We discuss these findings considering analyses of historical catalogues and available paleoseismological studies for the Sea of Marmara region to formulate reliable seismic hazard scenarios.

scholarly journals Neotectonics and Paleoseismicity of a Major Junction Between Two Strands of the Awatere Fault, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Dougal P M Mason
Keyword(s):  
New Zealand ◽  
Magnitude Estimate ◽  
Strike Slip ◽  
Fault System ◽  
Rupture Propagation ◽  
Coseismic Slip ◽  
The West ◽  
Fluvial Terraces ◽  
The Past ◽  
Earthquake Ruptures

<p><b>In northeastern South Island, New Zealand, obliquely-convergent relativemotion between the Pacific and Australian plates is accommodated by slip acrossactive dextral-oblique faults in the Marlborough fault system. The Awatere Fault isone of four principal active strike-slip faults within this plate boundary zone, andincludes two sections (the eastern and Molesworth sections) that have differentstrikes and that join across a complex fault junction in the upper Awatere Valley.</b></p> <p>Detailed mapping of the fault traces and measurement of 97 geomorphicdisplacements along the Awatere Fault in the vicinity of the fault junction show thatthe eastern and Molesworth sections of the fault intersect one another at a low angle(10-15º), at the eastern end of an internally faulted, elongate, ~15 km long and up to3 km wide fault wedge or sliver. The region between the fault sections is split by aseries of discontinuous, en-echelon scarps that are oriented from ~10º to 20-30ºclockwise from the principal fault sections. Based on other observations ofdiscontinuities in strike-slip earthquake ruptures around the globe, this low-angleintersection geometry suggests that the junction between these fault sections may notact as a significant barrier to earthquake rupture propagation. This interpretation ofthe mechanical significance of the fault junction to earthquake ruptures is counter toprevious suggestions, but is supported by new paleoseismic data from fourpaleoseismic trenches excavated on each side of the junction. In a new paleoseismictrench on the Molesworth section at Saxton River, 18 km to the west of the junction,up to ten surface-rupturing events in the past ~15 ka are recognised from 12radiocarbon ages and 1 optically stimulated luminescence age. In two new trencheson the eastern section near to Upcot Saddle, 12 km northeast of the fault junction,five events took place in the past 5.5 ka, based on 21 radiocarbon ages. Thischronology from Upcot Saddle is combined with data from two previous trencheslocated ~55 km to the northeast at Lake Jasper, to infer nine events on the easternsection since 8330-8610 cal. years B.P. These well-dated events on the easternsection are compared to those on the Molesworth section to the west of the faultjunction. At 95% confidence, five events on both sections have occurred withstatistical contemporaneity since ~6 ka B.P. These five events may have rupturedboth the eastern and Molesworth sections simultaneously, in accordance with the interpretation that the fault section junction does not arrest rupture propagation.</p> <p>Alternatively, these events may have been separate earthquakes that occurred withinthe statistical resolution provided by radiocarbon dating.</p> <p>The most recent event to rupture the eastern section was the Mw ~7.5 1848Marlborough earthquake. The coseismic slip distribution and maximum traceablelength of this surface rupture are calculated from the magnitude and distribution ofsmall, metre-scale geomorphic displacements attributable to this earthquake. Thesedata suggest this event ruptured >100-110 km of the eastern section, with meansurface displacement of 5.3 ±1.6 m. Based on these parameters, the momentmagnitude of this earthquake would be Mw 7.4-7.7. This magnitude estimate isindistinguishable from previous calculations that were based on attenuation ofshaking intensity isoseismals that were assigned from contemporary historicalaccounts of that earthquake. On the basis of similar rupture lengths and coseismicdisplacements, it is inferred that the penultimate event had a similar momentmagnitude to the 1848 earthquake.</p> <p>Horizontal displacement of a flight of 6 fluvial terraces at Saxton River by theMolesworth section of the Awatere Fault is constrained to have occurred at a nearconstantrate of 5.5 ±1.5 mm/a since ~15 ka B.P. These rates are based on two newoptically stimulated luminescence ages for the highest terrace treads of 14.5 ±1.5 and6.69 ±0.74 ka B.P. These rates are indistinguishable from recent strike-slip rateestimates for the eastern section of 5.6 ±1.1 and 6 ±2 mm/a. Comparing themagnitudes and ages of the terrace riser displacements at Saxton River to the timingof paleoearthquakes on the Molesworth section implies a mean per-eventdisplacement of 4.4 ±0.2 m since ~15 ka. The new terrace ages also record twoperiods of aggradation that post-date the Last Glacial Maximum.</p>

scholarly journals RECONSTRUCTION OF THE SLIP DISTRIBUTION ALONG THE WEST HELANSHAN FAULT, NORTHERN CHINA BASED ON HIGH-RESOLUTION TOPOGRAPHY

2020 ◽  
Vol XLIII-B2-2020 ◽  
pp. 1025-1031
Author(s):  
H. Bi ◽  
W. Zheng ◽  
Q. Lei ◽  
J. Zeng
Keyword(s):  
High Resolution ◽  
Active Fault ◽  
Northern China ◽  
Strike Slip ◽  
The Tibetan Plateau ◽  
The West ◽  
Rupture Length ◽  
Vertical Displacements ◽  
Significant Length ◽  
Very High

Abstract. The increasing wealthy of high-resolution topography allows for remotely measuring and analysing offset features and their associated surface slip distributions at a very high resolution and along a significant length of a fault, hence providing important insights into many aspects of the fault behaviour. The West Helanshan Fault is a Holocene active fault located at the junction of the Tibetan Plateau, Alashan, and Ordos blocks. Despite its special tectonic location, it has rarely been studied before. In this study, a 2-m-resolution DEM of the West Helanshan Fault was built from the high-resolution (0.5 m) WorldView-3 stereo satellite imagery based on the photogrammetry method, and a total of 181 strike-slip offsets and 201 vertical displacements were acquired along different segments of the fault. By statistical analysis of the offset observations, we conclude that at least six large paleoearthquakes have ruptured the fault, producing a minimum rupture length of ∼50 km, and the paleoearthquakes have followed a characteristic slip pattern with a coseismic strike slip of ∼3 m and a vertical slip of ∼1 m, corresponding to a geologic moment magnitude of 7.1–7.5.

scholarly journals Neotectonics and Paleoseismicity of a Major Junction Between Two Strands of the Awatere Fault, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Dougal P M Mason
Keyword(s):  
New Zealand ◽  
Magnitude Estimate ◽  
Strike Slip ◽  
Fault System ◽  
Rupture Propagation ◽  
Coseismic Slip ◽  
The West ◽  
Fluvial Terraces ◽  
The Past ◽  
Earthquake Ruptures

<p><b>In northeastern South Island, New Zealand, obliquely-convergent relativemotion between the Pacific and Australian plates is accommodated by slip acrossactive dextral-oblique faults in the Marlborough fault system. The Awatere Fault isone of four principal active strike-slip faults within this plate boundary zone, andincludes two sections (the eastern and Molesworth sections) that have differentstrikes and that join across a complex fault junction in the upper Awatere Valley.</b></p> <p>Detailed mapping of the fault traces and measurement of 97 geomorphicdisplacements along the Awatere Fault in the vicinity of the fault junction show thatthe eastern and Molesworth sections of the fault intersect one another at a low angle(10-15º), at the eastern end of an internally faulted, elongate, ~15 km long and up to3 km wide fault wedge or sliver. The region between the fault sections is split by aseries of discontinuous, en-echelon scarps that are oriented from ~10º to 20-30ºclockwise from the principal fault sections. Based on other observations ofdiscontinuities in strike-slip earthquake ruptures around the globe, this low-angleintersection geometry suggests that the junction between these fault sections may notact as a significant barrier to earthquake rupture propagation. This interpretation ofthe mechanical significance of the fault junction to earthquake ruptures is counter toprevious suggestions, but is supported by new paleoseismic data from fourpaleoseismic trenches excavated on each side of the junction. In a new paleoseismictrench on the Molesworth section at Saxton River, 18 km to the west of the junction,up to ten surface-rupturing events in the past ~15 ka are recognised from 12radiocarbon ages and 1 optically stimulated luminescence age. In two new trencheson the eastern section near to Upcot Saddle, 12 km northeast of the fault junction,five events took place in the past 5.5 ka, based on 21 radiocarbon ages. Thischronology from Upcot Saddle is combined with data from two previous trencheslocated ~55 km to the northeast at Lake Jasper, to infer nine events on the easternsection since 8330-8610 cal. years B.P. These well-dated events on the easternsection are compared to those on the Molesworth section to the west of the faultjunction. At 95% confidence, five events on both sections have occurred withstatistical contemporaneity since ~6 ka B.P. These five events may have rupturedboth the eastern and Molesworth sections simultaneously, in accordance with the interpretation that the fault section junction does not arrest rupture propagation.</p> <p>Alternatively, these events may have been separate earthquakes that occurred withinthe statistical resolution provided by radiocarbon dating.</p> <p>The most recent event to rupture the eastern section was the Mw ~7.5 1848Marlborough earthquake. The coseismic slip distribution and maximum traceablelength of this surface rupture are calculated from the magnitude and distribution ofsmall, metre-scale geomorphic displacements attributable to this earthquake. Thesedata suggest this event ruptured >100-110 km of the eastern section, with meansurface displacement of 5.3 ±1.6 m. Based on these parameters, the momentmagnitude of this earthquake would be Mw 7.4-7.7. This magnitude estimate isindistinguishable from previous calculations that were based on attenuation ofshaking intensity isoseismals that were assigned from contemporary historicalaccounts of that earthquake. On the basis of similar rupture lengths and coseismicdisplacements, it is inferred that the penultimate event had a similar momentmagnitude to the 1848 earthquake.</p> <p>Horizontal displacement of a flight of 6 fluvial terraces at Saxton River by theMolesworth section of the Awatere Fault is constrained to have occurred at a nearconstantrate of 5.5 ±1.5 mm/a since ~15 ka B.P. These rates are based on two newoptically stimulated luminescence ages for the highest terrace treads of 14.5 ±1.5 and6.69 ±0.74 ka B.P. These rates are indistinguishable from recent strike-slip rateestimates for the eastern section of 5.6 ±1.1 and 6 ±2 mm/a. Comparing themagnitudes and ages of the terrace riser displacements at Saxton River to the timingof paleoearthquakes on the Molesworth section implies a mean per-eventdisplacement of 4.4 ±0.2 m since ~15 ka. The new terrace ages also record twoperiods of aggradation that post-date the Last Glacial Maximum.</p>

Terrane amalgamation in the Clew Bay region, west of Ireland

1995 ◽  
Vol 132 (5) ◽  
pp. 485-501 ◽  
Author(s):  
J. D. Johnston ◽  
W. E. A. Phillips
Keyword(s):  
Strike Slip ◽  
Late Ordovician ◽  
Greenschist Facies ◽  
Fault System ◽  
Metamorphic Rocks ◽  
The West ◽  
Oblique Collision ◽  
Red Sandstone ◽  
North West ◽  
West Of Ireland

AbstractThe Caledonides of the west of Ireland provide a well-exposed and well-mapped example of an oblique collision zone. The east-northeast trending Deer Park and Achill Beg Fault system is a crustal scale ductile sinistral strike-slip duplex of late Ordovician age, imbricating late Precambrian granulite facies lower crustal rocks, near eclogite facies supracrustal rocks, up to amphibolite facies Dalradian metasedimentary rocks and greenschist facies Cambro-Ordovician rocks. This fault system is correlated with a pre-Devonian component of the Highland Boundary Fault system in southern Scotland. In the Clew Bay area, the high pressure-low temperature facies metamorphic rocks, in tectonic contact with greenschist facies Cambro-Ordovician rocks, are together interpreted as an accretionary prism complex related to northwestward directed subduction. Both of these are allocthonous terrains with respect to the Dalradian terrane to the north (North West Mayo). To the south, the Cambro-Ordovician rocks docked with a probable Dalradian block containing ultramafic intrusives (Deer Park Complex) during the late Ordovician. The Deer Park Complex and South Mayo Trough linked earlier, during the Arenig.Silurian and Lower-Middle Devonian redbed successions sit unconformably on the metamorphic rocks. Deposition and deformation of these cover rocks was controlled by oblique strike-slip movements on the Leek Fault whose strike swings from west-northwest to north-northeast, following earlier basement trends, as it is traced eastwards from Clew Bay. The Leek Fault System may be correlated with the Leannan Fault of northwest Donegal, a splay of the Great Glen Fault system of central Scotland. East of Clew Bay, this sinistral shear generated local dilation on the more northerly trending bend of the Leek Fault. Lower and Middle Old Red Sandstone redbeds were developed here. The west-northwest trend of the Leek Fault in Clew Bay acted as a compressional bend during these sinistral movements and transpressional southwest directed thrusting developed in Silurian rocks. Post-Middle Old Red Sandstone pre-late Tournaisian dextral displacement on the Leek Fault reversed this pattern with transtension in Clew Bay allowing intrusion of small carbonated peridotite bodies into Silurian rocks and easterly directed thrusting of Middle Old Red Sandstone rocks east of the Bay on the transpressional north-south bend.A tectonic model for the region is presented here. This model involves a northwestward directed subduction system, 150 to 750 km of Arenig sinistral strike slip movement, and eastwards insertion of the Connemara block with formation of the Ordovician South Mayo Trough as a pull-apart basin. Subsequently, a further 130 to 650 km eastward displacement of rocks took place south of the Deer Park Fault in later Ordovician times. The magnitudes of these estimates are directly proportional to an assumed maximum wavelength of 1500 km for promontories on the original Laurentian margin, and using the current juxtaposition of terranes, a minimum wavelength of 300 km is inferred.

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