Consolidation patterns during initiation and evolution of a plate-boundary decollement zone: Northern Barbados accretionary prism

Geology ◽  
1998 ◽  
Vol 26 (9) ◽  
pp. 811 ◽  
Author(s):  
J. Casey Moore ◽  
Adam Klaus ◽  
Nathan L. Bangs ◽  
Barbara Bekins ◽  
Christian J. Bücker ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Accretionary Prism

A Plate Too Far: Lessons Learned and Insight Gained from scientific and operational achievements during IODP Expedition 358 in the Nankai Trough.

2020 ◽  
Author(s):  
Adam Wspanialy ◽  
Sean Toczko ◽  
Nobu Eguchi ◽  
Lena Maeda ◽  
Kan Aoike ◽  
...  
Keyword(s):  
Real Time ◽  
Nankai Trough ◽  
Drilling Fluid ◽  
Plate Boundary ◽  
Accretionary Prism ◽  
Lessons Learned ◽  
Hole Drilling ◽  
Fault Mechanics ◽  
Boundary Fault ◽  
Novel Concept

<p>IODP Expedition 358 planned to access and sample the subducting plate boundary at the Nankai Trough, Japan, and commenced on 7 October 2018, and ended on 31 March 2019, marking the ultimate stage of the NanTroSEIZE project. The goal was to drill down to the plate boundary fault, about 5 km below the ocean floor, where >8M earthquakes occur regularly at every 100–150 years. The successful completion would have represented the deepest borehole in the history of scientific ocean drilling and ultimately greatly deepen our understanding about fault mechanics, earthquake inception and tsunami generation processes.</p><p>The IODP Expedition 358 intended to access the plate boundary fault zone system through deepening the previously drilled and suspended C0002P hole. The original operational objective of the Exp 358 was to reach a total depth of 7267.5 mbrt (+/- 5200 mbsf) in 4 drilled sections. Previous major riser drilling efforts during the IODP Expeditions 338 and 348 advanced the main riser hole at Site C0002 (Hole C0002F/N/P) to 3058.5 mbsf meters below sea floor (mbsf). Extensive downhole logging data and limited intervals of core were collected during those expeditions.</p><p>Due to the nature of the drilling operation and the anticipated challenges ahead, JAMSTEC adopted oil & gas industry drilling standards and performed two detailed Drilling Well on Paper (DWOP) workshops as part of the very rigorous preparatory stage. Great deal of time was spent on selecting new and state-of-the-art drilling/circulating techniques, logging tools, bits and drilling fluid formulation including a new mud sealant additive “FracSeal” to make sure borehole integrity issues can be minimized as much as possible. Drilling stages seen implementation of a novel concept of near real-time geomechanics to continuously monitor and assess borehole integrity.</p><p>The challenges born from side-tracking near the bottom of the previously drilled Hole C0002P (2014 Exp. 348), proved greater than the multi-disciplinary teams expected and the overall objectives set for Exp.358 were not achieved. Nevertheless, despite the significant problems seen during several attempts, the hole was deepened 204 m. This is a minor success and it is believed, once away from the highly damaged area of the C0002P hole, drilling can produce a high-integrity hole following excellent communication and recommendations between drilling and scientific teams during complex drilling operations, especially in complex environments such as the Nankai Accretionary Prism.</p><p>Despite not achieving the ultimate goal of the expedition, the implemented industry drilling standards, real-time surveillance system, real time geomechanics, improved and strict communication protocols, and integrating both scientific and drilling teams have demonstrated their value and should become standard practice during future IODP/ICDP operations.</p>

scholarly journals Post-seismic response of the outer accretionary prism after the 2010 Maule earthquake, Chile

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 13-32 ◽  
Author(s):  
Anne M. Tréhu ◽  
Alexander de Moor ◽  
José Mieres Madrid ◽  
Miguel Sáez ◽  
C. David Chadwell ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Plate Boundary ◽  
Low Frequency ◽  
Accretionary Prism ◽  
Absolute Pressure ◽  
Ocean Bottom ◽  
Intermediate Band ◽  
Outer Rise ◽  
Maule Earthquake ◽  
Seafloor Pressure

Abstract To investigate the dynamic response of the outer accretionary prism updip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (Chile), 10 ocean-bottom seismometers (OBSs) were deployed from May 2012 to March 2013 in a small network with an inter-instrument spacing of 7–10 km. Nine were recovered, with four recording data from intermediate-band three-component seismometers and differential pressure gauges, and five recording data from absolute pressure gauges (APGs). All instruments were also equipped with fluid flow meters designed to detect very low rates of flow into or out of the seafloor. We present hypocenters for local earthquakes that have S-P times <17 s (i.e., within ∼125 km of the network), with a focus on events located beneath or near the network. Most of the seismicity occurred either near the boundary between the active accretionary prism and continental basement or in the outer rise seaward of the trench. For many outer-rise earthquakes, the P and S arrivals are followed by a distinctive T-phase arrival. Very few earthquakes, and none located with hypocenters deemed “reliable,” were located within the active accretionary prism or on the underlying plate boundary. Nonvolcanic tremor-like pulses and seafloor pressure transients (but no very-low-frequency earthquakes or fluid flow) were also detected. Many of the tremor observations are likely T-phases or reverberations due to soft seafloor sediments, although at least one episode may have originated within the accretionary prism south of the network. The transient seafloor pressure changes were observed simultaneously on three APGs located over the transition from the active prism to the continental basement and show polarity changes over short distances, suggesting a shallow source. Their duration of several hours to days is shorter than most geodetic transients observed using onshore GPS networks. The results demonstrate the need for densely spaced and large-aperture OBS networks equipped with APGs for understanding subduction zone behavior.

scholarly journals Geologic controls on up-dip and along-strike propagation of slip during subduction zone earthquakes from a high-resolution seismic reflection survey across the northern limit of slip during the 2010 Mw 8.8 Maule earthquake, offshore Chile

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1751-1773 ◽  
Author(s):  
Anne M. Tréhu ◽  
Bridget Hass ◽  
Alexander de Moor ◽  
Andrei Maksymowicz ◽  
Eduardo Contreras-Reyes ◽  
...  
Keyword(s):  
High Resolution ◽  
Subduction Zone ◽  
Seismic Reflection ◽  
Plate Boundary ◽  
Accretionary Prism ◽  
Structural Heterogeneity ◽  
Deformation Front ◽  
Maule Earthquake ◽  
Subduction Zone Earthquakes ◽  
Trench Sediments

Abstract A grid of closely spaced, high-resolution multichannel seismic (MCS) reflection profiles was acquired in May 2012 over the outer accretionary prism up dip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (offshore Chile) to complement a natural-source seismic experiment designed to monitor the post-earthquake response of the outer accretionary prism. We describe the MCS data and discuss the implications for the response of the accretionary prism during the earthquake and for the long-term evolution of the margin. The most notable observation from the seismic reflection survey is a rapid north-to-south shift over a short distance from nearly total frontal accretion of the trench sediments to nearly total underthrusting of undeformed trench sediments that occurs near the northern edge of slip in the 2010 earthquake. Integrating our structural observations with other geological and geophysical observations, we conclude that sediment subduction beneath a shallow décollement is associated with propagation of slip to the trench during great earthquakes in this region. The lack of resolvable compressive deformation in the trench sediment along this segment of the margin indicates that the plate boundary here is very weak, which allowed the outer prism to shift seaward during the earthquake, driven by large slip down dip. The abrupt shift from sediment subduction to frontal accretion indicates a stepdown in the plate boundary fault, similar to the stepovers that commonly arrest slip propagation in strike-slip faults. We do not detect any variation along strike in the thickness or reflective character of the trench sediments adjacent to the change in deformation front structure. This change, however, is correlated with variations in the morphology and structure of the accretionary prism that extend as far as 40 km landward of the deformation front. We speculate that forearc structural heterogeneity is the result of subduction of an anomalously shallow or rough portion of plate that interacted with and deformed the overlying plate and is now deeply buried. This study highlights need for three-dimensional structural images to understand the interaction between geology and slip during subduction zone earthquakes.

Seismic expression of shallow structures in active tectonic settings in New Zealand

1989 ◽  
Vol 20 (2) ◽  
pp. 287
Author(s):  
C.D. Cape ◽  
R.M. O'Connor ◽  
J.M. Ravens ◽  
D.J. Woodward
Keyword(s):  
New Zealand ◽  
Plate Boundary ◽  
Accretionary Prism ◽  
Seismic Profile ◽  
Thrust Fault ◽  
Strike Slip ◽  
Normal Faults ◽  
Thrust Faults ◽  
Seismic Reflection Data ◽  
Reflection Data

Late Cenozoic deformation along the Australian/Pacific plate boundary is seen in onshore New Zealand as zones characterised by extension- or transcurrent- or contraction-related structures. High-resolution multichannel seismic reflection data were acquired in several of these tectonic zones and successfully reveal the shallow structures within them. Thirty kilometres of dynamite reflection data in the Rangitaiki Plains, eastern Bay of Plenty, define a series of NE-trending normal faults within this extensional back-arc volcanic region. The data cross surface ruptures activated during the 1987 Edgecumbe earthquake. In the southern North Island, a 20 km Mini-Sosie? seismic profile details the Quaternary sedimentation history and reveals the structure of the active strike-slip and thrust fault systems that form the western and eastern edges of the Wairarapa basin, respectively. This basin is considered to sit astride the boundary between a zone of distributed strike-slip faults and an active accretionary prism. In the Nelson area, northwestern South Island, previously unrecognised low-angle thrust faults of Neogene or Quaternary age are seen from Mini-Sosie data to occur at very shallow depths. Crustal shortening here was previously thought to arise from movement on high-angle reverse faults, and the identification of these low-angle faults has prompted a reassessment of that model. A grid of 18 km of Mini-Sosie seismic data from the central eastern South Island delineates Neogene or Quaternary thrust faults in Cenozoic sediments. The thrusts are interpreted as reactivated Early Eocene normal faults, and the thrust fault geometry is dominated by these older structures.

scholarly journals MAJOR PALEOGEOGRAPHIC, TECTONIC AND GEODYNAMIC CHANGES FROM THE LAST STAGE OF THE HELLENIDES TO THE ACTUAL HELLENIC ARC AND TRENCH SYSTEM

2017 ◽  
Vol 43 (1) ◽  
pp. 72 ◽  
Author(s):  
D. Papanikolaou
Keyword(s):  
Shear Zone ◽  
Late Miocene ◽  
Plate Boundary ◽  
Aegean Sea ◽  
Accretionary Prism ◽  
Driving Mechanism ◽  
The South ◽  
The North ◽  
Hellenic Arc ◽  
Surrounding Areas

Present day location and geometry of the Hellenic arc and trench system is only a small portion of the previously developed Hellenic arc that created the Hellenides orogenic system. The timing of differentiation is constrained in Late Miocene, when the arc was divided in a northern and a southern segment. This is based on: a) the dating of the last compressive structures observed all along the Hellenides during Oligocene to Middle-Late Miocene, b) on the time of initiation of the Kephalonia transform fault, c) on the time of opening of the North Aegean Basin and d) on the time of opening of new arc parallel basins in the south and new transverse basins in the central shear zone, separating the rapidly moving southwestwards Hellenic subduction system from the slowly converging system of the Northern Hellenides. The driving mechanism of the arc differentiation is the heterogeneity produced by the different subducting slabs in the north (continental) and in the south (oceanic) and the resulted shear zone because of the retreating plate boundary producing a roll back mechanism in the present arc and trench system. The paleogeographic reconstructions of the Hellenic arc and surrounding areas show the shortening of the East Mediterranean oceanic area, following the slow convergence rate of the European and African plates plus the localised shortening following the rapid Hellenic subduction rate. The result is that the frontal parts of the accretionary prism developed in front of the Hellenic arc have reached the African continent in Cyrenaica whereas on the two sides the basinal parts of the Ionian and Levantine basins are still preserved before their final subduction and closure. The extension produced in the upper plate has resulted in the subsidence of the Aegean Sea and the creation of several neotectonic basins in southern continental Greece in contrast to the absence of new basins in the northern segment since Late Miocene.

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