scholarly journals Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity

2021 ◽  
Vol 9 ◽  
Author(s):  
Melissa O. Anderson ◽  
Chantal Norris-Julseth ◽  
Kenneth H. Rubin ◽  
Karsten Haase ◽  
Mark D. Hannington ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Plate Boundary ◽  
Structural Evolution ◽  
Strike Slip ◽  
Normal Faults ◽  
Geologic Mapping ◽  
Centroid Moment Tensor ◽  
Lau Basin ◽  
Fault Kinematics ◽  
Back Arc

The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two notable features of the NE Lau Basin: 1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and 2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ∼120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, the Riedel structures identified in this study directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism.

The Global Importance of Continental Seismic Sequences

2020 ◽  
Author(s):  
Richard Walters ◽  
Tim Craig ◽  
Laura Gregory ◽  
Russell Azad Khan
Keyword(s):  
Structural Control ◽  
Initial Conditions ◽  
Moment Tensor ◽  
Central Italy ◽  
Relative Number ◽  
Strike Slip ◽  
Normal Faults ◽  
Centroid Moment Tensor ◽  
Multiple Faults ◽  
Seismic Sequences

<p>Large continental earthquakes necessarily involve cascading rupture of multiple faults or segments (e.g. El Mayor-Cucapah 2010). But these same critically-stressed systems sometimes rupture in drawn-out sequences of smaller earthquakes over days or years (e.g. Central Italy 2016), instead of in a single large event. Due to the similarity in the initial conditions of both scenarios, seismic sequences may be considered as ‘failed’ multi-segment earthquakes, whereby cascading rupture is prematurely halted before all available slip deficit is released.</p><p>These two modes of strain-release have vastly different implications for seismic hazard. Recent work on the 2016 Central Italy earthquake sequence, which is the first seismic sequence to be studied with modern high-quality geodetic and seismological datasets, showed that complexity in fault structure appeared to exercise a dual control on both the timing and sizes of events throughout this sequence. However, it is unclear if this structural control is common for all continental seismic sequences, how important seismic sequences are for the global seismic moment budget, and how this contribution to moment budget may vary between different tectonic regions.</p><p>Here we select shallow crustal continental earthquakes from the Global Centroid Moment Tensor catalog, and identify seismic sequences as agglomerates of clustered pairs of earthquakes where the summed moment (M<sub>0</sub>) of all aftershocks is greater than 50% of the M<sub>0</sub> of the first event in the sequence. We analyse the relative number of seismic sequences compared to other earthquakes for normal, reverse, and strike-slip faulting regions, and also calculate the relative M<sub>0</sub> release of seismic sequences and other earthquakes in these three regimes.</p><p>We find that although seismic sequences are equally common by number in all continental tectonic regimes, seismic sequences account for a much higher proportion of M<sub>0</sub> release for normal faults (~20%) than for reverse faults (~10%), with strike-slip faults intermediate between these two end-members. We also find that the proportion of M<sub>0</sub> release in seismic sequences is higher for events that occur in regions characterised by a diversity of different earthquake types (e.g. both reverse and strike-slip faulting) than for events that occur in regions characterised by a single earthquake type (e.g. strike-slip faulting only). Together these findings imply that complexity of fault network is an important factor in controlling the occurrence of large-M<sub>0</sub> seismic sequences, and that ‘failed’ multi-segment earthquakes and therefore large-M<sub>0</sub> seismic sequences are more likely to occur in regions with complex fault networks.</p>

scholarly journals Contact of the Samoan Plume with the Tonga Subduction from Intermediate and Deep-Focus Earthquakes

2021 ◽  
Author(s):  
Pavla Hrubcová ◽  
Václav Vavryčuk
Keyword(s):  
Moment Tensor ◽  
Plate Boundary ◽  
S Wave ◽  
Low Velocity ◽  
Centroid Moment Tensor ◽  
S Waves ◽  
Velocity Anomalies ◽  
Deep Focus ◽  
Tectonic Features ◽  
Back Arc

AbstractThe Tonga subduction zone in the south-west Pacific is the fastest convergent plate boundary in the world with the most active mantle seismicity. This zone shows unique tectonic features including Samoan volcanic lineament of plume-driven origin near the northern rim of the Tonga subducting slab. The proximity of the Samoa hotspot to the slab is enigmatic and invokes debates on interactions between the Samoa plume and the Tonga subduction. Based on long-term observations of intermediate and deep-focus Tonga earthquakes reported in the Global Centroid Moment Tensor (CMT) catalog, we provide novel detailed imaging of this region. Accurate traveltime residua of the P- and S-waves recorded at two nearby seismic stations of the Global Seismographic Network are inverted for the P- and S-wave velocities and their ratio and reveal their pronounced lateral variations. In particular, they differ for the southern and northern parts of the Tonga subduction region. While no distinct anomalies are detected in the southern Tonga segment, striking low-velocity anomalies associated with a high Vp/Vs ratio are observed in the northern Tonga segment close to the Samoa plume. These anomalies spread through the whole upper mantle down to depths of ~ 600 km. Together with the fast extension of the northern back-arc Lau Basin, slab deformation and geochemical enrichment in the northern Tonga region, they trace deep-seated magmatic processes and evidence an interaction of the Tonga subduction with the Samoa plume.

scholarly journals New Updated Classification of Shallow Earthquakes Based on Faulting Style

2020 ◽  
pp. 103-111
Author(s):  
Emad Abulrahman Mohammed Salih Al-Heety
Keyword(s):  
Return Period ◽  
Moment Tensor ◽  
Focal Depth ◽  
Strike Slip ◽  
Shallow Depth ◽  
Main Trend ◽  
Maximum Magnitude ◽  
Centroid Moment Tensor ◽  
Significant Information

Earthquakes occur on faults and create new faults. They also occur on  normal, reverse and strike-slip faults. The aim of this work is to suggest a new unified classification of Shallow depth earthquakes based on the faulting styles, and to characterize each class. The characterization criteria include the maximum magnitude, focal depth, b-constant value, return period and relations between magnitude, focal depth and dip of fault plane. Global Centroid Moment Tensor (GCMT) catalog is the source of the used data. This catalog covers the period from Jan.1976 to Dec. 2017. We selected only the shallow (depth less than 70kms) pure, normal, strike-slip and reverse earthquakes (magnitude ≥ 5) and excluded the oblique earthquakes. The majority of normal and strike-slip earthquakes occurred in the upper crust, while the reverse earthquakes occurred throughout the thickness of the crust. The main trend for the derived b-values for the three classes was: b normal fault>bstrike-slip fault>breverse fault.  The mean return period for the normal earthquake was longer than that of the strike-slip earthquakes, while the reverse earthquakes had the shortest period. The obtained results report the relationship between the magnitude and focal depth of the normal earthquakes. A negative significant correlation between the magnitude and dip class for the normal and reverse earthquakes is reported. Negative and positive correlation relations between the focal depth and dip class were recorded for normal and reverse earthquakes, respectively. The suggested classification of earthquakes provides significant information to understand seismicity, seismtectonics, and seismic hazard analysis.

scholarly journals Superposition of two kinematically distinct extensional phases in southern Death Valley: Implications for extensional tectonics

Geosphere ◽  
2021 ◽  
Author(s):  
Z.D. Fleming ◽  
T.L. Pavlis ◽  
S. Canalda
Keyword(s):  
Early Period ◽  
Rock Avalanche ◽  
Strike Slip ◽  
Death Valley ◽  
Normal Faults ◽  
Geologic Mapping ◽  
The North ◽  
Transcurrent Deformation ◽  
Two Phases

Geologic mapping in southern Death Valley, California, demonstrates Mesozoic contractional structures overprinted by two phases of Neogene extension and contemporaneous strike-slip deformation. The Mesozoic folding is most evident in the middle unit of the Noonday Formation, and these folds are cut by a complex array of Neogene faults. The oldest identified Neogene faults primarily displace Neoproterozoic units as young as the Johnnie Formation. However, in the northernmost portion of the map area, they displace rocks as young as the Stirling Quartzite. Such faults are seen in the northern Ibex Hills and con­sist of currently low- to moderate-angle, E-NE– dipping normal faults, which are folded about a SW-NE–trending axis. We interpret these low-angle faults as the product of an early, NE-SW extension related to kinematically similar deformation recognized to the south of the study area. The folding of the faults postdates at least some of the extension, indicating a component of syn-exten­sional shortening that is probably strike-slip related. Approximately EW-striking sinistral faults are mapped in the northern Saddlepeak Hills. However, these faults are kinematically incompatible with the folding of the low-angle faults, suggesting that folding is related to the younger, NW-SE extension seen in the Death Valley region. Other faults in the map area include NW- and NE-striking, high-angle normal faults that crosscut the currently low-angle faults. Also, a major N-S–striking, oblique-slip fault bounds the eastern flank of the Ibex Hills with slickenlines showing rakes of <30°, which together with the map pattern, suggests dextral-oblique movement along the east front of the range. The exact timing of the normal faulting in the map area is hampered by the lack of geochronology in the region. However, based on the map relationships, we find that the older extensional phase predates an angular unconformity between a volcanic and/or sedimentary succession assumed to be 12–14 Ma based on correlations to dated rocks in the Owlshead Mountains and overlying rock-avalanche deposits with associated sedimentary rocks that we correlate to deposits in the Amargosa Chaos to the north, dated at 11–10 Ma. The mechanism behind the folding of the northern Ibex Hills, including the low- angle faults, is not entirely clear. However, transcurrent systems have been proposed to explain extension-parallel folding in many extensional terranes, and the geometry of the Ibex Hills is consistent with these models. Collectively, the field data support an old hypothesis by Troxel et al. (1992) that an early period of SW-NE extension is prominent in the southern Death Valley region. The younger NW-SE extension has been well documented just to the north in the Black Mountains, but the potential role of this earlier extension is unknown given the complexity of the younger deformation. In any case, the recognition of earlier SW-NE extension in the up-dip position of the Black Mountains detachment system indicates important questions remain on how that system should be reconstructed. Collectively, our observations provide insight into the stratigraphy of the Ibex Pass basin and its relationship to the extensional history of the region. It also highlights the role of transcurrent deformation in an area that has transitioned from extension to transtension.

scholarly journals Neotectonics of the Owen Fracture Zone (NW Indian Ocean): Structural evolution of an oceanic strike-slip plate boundary

2011 ◽  
Vol 12 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
M. Rodriguez ◽  
M. Fournier ◽  
N. Chamot-Rooke ◽  
P. Huchon ◽  
J. Bourget ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Fracture Zone ◽  
Plate Boundary ◽  
Structural Evolution ◽  
Strike Slip

Main fault systems of the Soviet Far East

1986 ◽  
Vol 317 (1539) ◽  
pp. 267-275 ◽  
Keyword(s):  
Active Continental Margin ◽  
Far East ◽  
Structural Evolution ◽  
Acute Angle ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Late Mesozoic ◽  
Early Mesozoic ◽  
Main Fault

The analysis of the distribution of thrusts, normal faults and strike-slip faults of various ages has allowed us to determine the character of lithospheric block displacements in the Soviet Far East. The early Mesozoic, late Mesozoic and Cainozoic kinematics were each essentially different. The Early Mesozoic Dzhagdinsk fault system appeared as a result of the collision of the Bureinsk-Khankaisk microcontinent with the Siberian continent. The largest faults of the system are neither longstanding nor deep but were formed during the latest stage of the structural evolution. The multistage formation of the faults of the Dzhagdinsk system is conditioned by its position at the margin of the continent. The late Mesozoic faults are mainly strike-slip faults caused by the subduction of the oceanic crust at an acute angle with respect to the strike of the active continental margin. The Cainozoic faults were formed under compression on the boundary between the Siberian platform and the Bureinsk massif, but under tension in the east of the region.

scholarly journals ANALISIS SEISMOGRAM TIGA KOMPONEN TERHADAP MOMENT TENSOR GEMPA BUMI DI MANOKWARI PAPUA 03 JANUARI 2009

2012 ◽  
Author(s):  
Irwan Setyowidodo, Bagus Jaya Santosa
Keyword(s):  
Fault Plane ◽  
Moment Tensor ◽  
Strike Slip ◽  
Centroid Moment Tensor

Penelitian ini melakukan analisis inversi waveform 3 komponen terhadap data gempa bumi yang  terjadi  di  Manokwari  Papua  pada  tanggal  3  Januari  2009  pukul  19:43:55  GMT  dengan magnitude  7.1  Mw  yang  episentrumnya  berada  pada  lattitude  -0.70541,  longitude  125.8455  dan kedalaman 25 km. Data yang digunakan dalam penelitian ialah, data seismik lokal yang diunduh dari data  gempa  IA.  Selanjutnya  dilakukan  proses   inversi  data  waveform  tiga  komponen  dengan menggunakan  metode  iterasi  dekonvolusi.  Metode  ini  diimplementasikan  dalam  software  ISOLA yang  dikembangkan   untuk  mendapatkan  parameter-parameter  sumber  gempa  bumi.  Parameter- parameter  gempa ini tergambarkan dalam Centroid Moment Tensor dan parameter sesar penyebab gempa. Selanjutnya, hasil parameter-patameter  tersebut digunakan untuk  mengetahui arah  patahan yang sebenarnya (fault-plane) dengan menggunakan metode H-C. Seismogram sintetik dihitung dengan ISOLA yang inputnya adalah model bumi dan data seismogram yang  direkam  oleh  stasiun  seismologi  BAK,  LBM  dan  JAY.  Hasil   interpretasi  atas  analisis seismogram   waveform   tiga   komponen   menunjukkan   bahwa   orientasi   bidang   patahan   gempa Manokwari Papua pada tanggal 3 Januari 2009 memiliki sudut dip 54o       terhadap bidang  horizontal yang menyebabkan zona patahan di daerah tersebut mudah bergeser dan mudah terjadi gempa. Hasil analisis  ini  diketahui  bahwa  sesar  penyebab  gempa  bumi  ini  ialah  sesar  strike-slip  oblique  yang bergerak dari  arah barat  laut - tenggara. Sumber  gempa  bumi  yang terjadi tersebut terjadi akibat aktivitas Sesar Sorong yang terdapat di bagian utara Manokwari.<br /><br /><br /><br />

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