The geology and evolution of the Pinchi Fault Zone at Pinchi Lake, central British Columbia

1977 ◽  
Vol 14 (6) ◽  
pp. 1324-1342 ◽  
Author(s):  
I. A. Paterson
Keyword(s):  
Fault Zone ◽  
Subduction Zones ◽  
High Pressures ◽  
Metamorphic Grade ◽  
Fault System ◽  
Late Triassic ◽  
Transform Fault ◽  
The West ◽  
Early Mesozoic ◽  
Complex Fault

At Pinchi Lake, the Pinchi Fault Zone separates the early Mesozoic Takla Group to the east from the late Paleozoic Cache Creek Group to the west. Between these regions a complex fault system involves a series of elongate fault-bounded blocks of contrasting lithology and metamorphic grade. These blocks consist of: (a) highly deformed aragonite–dolomite limestone and blueschist, (b) pumpellyite–aragonite greenstone, (c) a harzburgite–gabbro–diabase–basalt ophiolite sequence, (d) serpentinized alpine ultramafite, and (e) Cretaceous (?) conglomerate. The blueschist probably formed at 8–12 kbar (8 × 105–12 × 105 kPa) and 225–325 °C during a penetrative early deformation which was closely followed by a later deformation associated with a Late Triassic uplift and cooling event. The ophiolite sequence is overlain by Late Triassic sediments which locally contain aragonite suggesting that at least part of the Takla Group may have also undergone high pressure – low temperature metamorphism.The evolution of the 450 km fault zone is discussed and a model is proposed which involves right lateral transform faulting on the Pinchi Fault and underthrusting along northerly dipping subduction zones during the Late Triassic. The blueschist formed at high pressures in such a subduction zone and leaked to the surface in zones of low pressure along an active transform fault.

Timing of arrival of the Avalon Zone in the northeastern Appalachians: a new look at the Straddling Granite

1982 ◽  
Vol 19 (5) ◽  
pp. 1088-1094 ◽  
Author(s):  
Peter N. Elias ◽  
D. F. Strong
Keyword(s):  
Fault Zone ◽  
Early Carboniferous ◽  
Fault System ◽  
The West ◽  
Plutonic Rocks ◽  
Indian Point ◽  
Intrusive Suite ◽  
Timing Of Arrival ◽  
New Look

The "Straddling Granite" was previously thought to straddle the Hermitage Bay – Dover fault system, which marks the boundary between the Avalon and Gander Zones of eastern Newfoundland, and hence to fix the earliest juxtaposition of these two zones before 504 ± 12 Ma. More detailed investigation shows that these rocks are divisible into two distinct geochemical suites, the Indian Point Granite to the west and the Hardy's Cove intrusive suite to the east. Of the samples that provided the 504 Ma isochron, five were obtained from the Hardy's Cove suite and one from within the fault zone; hence the isochron must be taken as representing only a typical date for plutonic rocks within the Avalon Zone. The Indian Point Granite intrudes the Gaultois Granite, dated at 350 ± 18 Ma, and is thus considerably younger than the Hardy's Cove suite. These observations now allow for juxtaposition of the Avalon and Gander Zones to have been as late as Early Carboniferous.

Crustal Architecture of Puerto Rico Using Body-Wave Seismic Tomography and High-Resolution Earthquake Relocation

2021 ◽  
Author(s):  
Guoqing Lin ◽  
Victor A. Huerfano ◽  
Wenyuan Fan
Keyword(s):  
Puerto Rico ◽  
Fault Zone ◽  
Wave Velocity ◽  
Velocity Ratio ◽  
Fault System ◽  
Velocity Models ◽  
Complex Fault ◽  
3D Velocity Model ◽  
Waveform Cross Correlation ◽  
The Caribbean

Abstract Puerto Rico is a highly seismically active island, where several damaging historical earthquakes have occurred and frequent small events persist. It situates at the boundary between the Caribbean and North American plates, featuring a complex fault system. Here, we investigate the seismotectonic crustal structure of the island by interpreting the 3D compressional-wave velocity VP and compressional- to shear-wave velocity ratio VP/VS models and by analyzing the distribution of the relocated earthquakes. The 3D velocity models are obtained by applying the simul2000 tomographic inversion algorithm based on the phase arrivals recorded by the Puerto Rico seismic network. We find high-VP and low-VP/VS anomalies in the eastern and central province between the Great Northern Puerto Rico fault zone and the Great Southern Puerto Rico fault zone, correlating with the Utuado pluton. Further, there are low-VP anomalies beneath both the Great Southern Puerto Rico fault zone and the South Lajas fault, indicating northerly dipping structures from the southwest to the northwest of the island. We relocate 19,095 earthquakes from May 2017 to April 2021 using the new 3D velocity model and waveform cross-correlation data. The relocated seismicity shows trends along the Investigator fault, the Ponce faults, the Guayanilla rift, and the Punta Montalva fault. The majority of the 2019–2021 Southwestern Puerto Rico earthquakes are associated with the Punta Montalva fault. Earthquakes forming 17° northward-dipping structures at various depths possibly manifest continuation of the Muertos trough, along which the Caribbean plate is being subducted beneath the Puerto Rico microplate. Our results show complex fault geometries of a diffuse fault network, suggesting possible subduction process accommodated by faults within a low-velocity zone.

scholarly journals Seismic investigation of an active ocean–continent transform margin: the interaction between the Swan Islands Fault Zone and the ultraslow-spreading Mid-Cayman Spreading Centre

2019 ◽  
Vol 219 (1) ◽  
pp. 159-184 ◽  
Author(s):  
C Peirce ◽  
A H Robinson ◽  
A M Campbell ◽  
M J Funnell ◽  
I Grevemeyer ◽  
...  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Fault Zone ◽  
Lower Crust ◽  
P Wave ◽  
Fault System ◽  
Transform Fault ◽  
Apparent Lack ◽  
The North ◽  
Transform Margin

SUMMARY The Swan Islands Transform Fault (SITF) marks the southern boundary of the Cayman Trough and the ocean–continent transition of the North American–Caribbean Plate boundary offshore Honduras. The CAYSEIS experiment acquired a 180-km-long seismic refraction and gravity profile across this transform margin, ∼70 km to the west of the Mid-Cayman Spreading Centre (MCSC). This profile shows the crustal structure across a transform fault system that juxtaposes Mesozoic-age continental crust to the south against the ∼10-Myr-old ultraslow spread oceanic crust to the north. Ocean-bottom seismographs were deployed along-profile, and inverse and forward traveltime modelling, supported by gravity analysis, reveals ∼23-km-thick continental crust that has been thinned over a distance of ∼70 km to ∼10 km-thick at the SITF, juxtaposed against ∼4-km-thick oceanic crust. This thinning is primarily accommodated within the lower crust. Since Moho reflections are not widely observed, the 7.0 km s−1 velocity contour is used to define the Moho along-profile. The apparent lack of reflections to the north of the SITF suggests that the Moho is more likely a transition zone between crust and mantle. Where the profile traverses bathymetric highs in the off-axis oceanic crust, higher P-wave velocity is observed at shallow crustal depths. S-wave arrival modelling also reveals elevated velocities at shallow depths, except for crust adjacent to the SITF that would have occupied the inside corner high of the ridge-transform intersection when on axis. We use a Vp/Vs ratio of 1.9 to mark where lithologies of the lower crust and uppermost mantle may be exhumed, and also to locate the upper-to-lower crustal transition, identify relict oceanic core complexes and regions of magmatically formed crust. An elevated Vp/Vs ratio suggests not only that serpentinized peridotite may be exposed at the seafloor in places, but also that seawater has been able to flow deep into the crust and upper mantle over 20–30-km-wide regions which may explain the lack of a distinct Moho. The SITF has higher velocities at shallower depths than observed in the oceanic crust to the north and, at the seabed, it is a relatively wide feature. However, the velocity–depth model subseabed suggests a fault zone no wider than ∼5–10 km, that is mirrored by a narrow seabed depression ∼7500 m deep. Gravity modelling shows that the SITF is also underlain, at >2 km subseabed, by a ∼20-km-wide region of density >3000 kg m−3 that may reflect a broad region of metamorphism. The residual mantle Bouguer anomaly across the survey region, when compared with the bathymetry, suggests that the transform may also have a component of left-lateral trans-tensional displacement that accounts for its apparently broad seabed appearance, and that the focus of magma supply may currently be displaced to the north of the MCSC segment centre. Our results suggest that Swan Islands margin development caused thinning of the adjacent continental crust, and that the adjacent oceanic crust formed in a cool ridge setting, either as a result of reduced mantle upwelling and/or due to fracture enhanced fluid flow.

Overturned Nicola and Ashcroft strata and their relation to the Cache Creek Group, Southwestern Intermontane Belt, British Columbia

1978 ◽  
Vol 15 (1) ◽  
pp. 99-116 ◽  
Author(s):  
William B. Travers
Keyword(s):  
Lower Jurassic ◽  
Upper Triassic ◽  
Late Triassic ◽  
Turbidity Currents ◽  
Alkaline Magmatism ◽  
Thick Section ◽  
Calc Alkaline ◽  
The West ◽  
Early Mesozoic ◽  
Eastern Edge

The Lower Jurassic, Ashcroft Formation contains a thick section of carbonaceous marine shale and a few graded sandstones. Along the south and east margins of the Ashcroft Basin, Ashcroft strata rest unconformably on calc-alkaline and alkaline volcanic flows and sediments of the Upper Triassic, Nicola Group. On the west margin Nicola and Ashcroft strata lie against mélange of the Cache Creek Group. This contact is faulted in some places, but it may be a depositional unconformity elsewhere.South of Cache Creek village, overturned allochthons of Nicola strata were placed on top of Ashcroft beds in Early Jurassic time before Ashcroft sediments were lithified. Turbidity currents flowed southeast contemporaneous with sliding or thrusting of allochthons.Near the Guichon Creek Batholith, the Ashcroft Formation contains a disconformity that separates Sinemurian–Pliensbachian from Callovian strata. However, in the western part of the Ashcroft basin strata appear continuous from Sinemurian–Pliensbachian to Callovian. The Guichon Creek Batholith was emplaced into Nicola strata along the eastern edge of the Ashcroft Basin about 200 Ma ago (late Sinemurian*) and was quickly unroofed to provide granitic debris to the basin.The Ashcroft Basin appears to have been an early Mesozoic outer arc basin. It formed seaward of calc-alkaline magmatism and landward of and possibly on top of a mélange. Middle or Late Triassic radiolaria found in the Cache Creek show that deformation of the mélange took place as late as Late Triassic time. Arc-directed thrusting and sliding may be gravity processes due to elevation of the outer arc ridge during subduction.

scholarly journals The 29 March 2017 Yuzhno-Ozernovskoe Kamchatka Earthquake: Fault Activity in An Extension of the East Kamchatka Fault Zone as Constrained by InSAR Observations

2020 ◽  
Vol 110 (3) ◽  
pp. 1101-1114
Author(s):  
Magdalena S. Vassileva ◽  
Mahdi Motagh ◽  
Thomas R. Walter ◽  
Hans-Ulrich Wetzel ◽  
Sergey L. Senyukov
Keyword(s):  
Synthetic Aperture Radar ◽  
Fault Zone ◽  
Subduction Zones ◽  
Synthetic Aperture ◽  
Fault System ◽  
Coseismic Deformation ◽  
Reverse Fault ◽  
Nonlinear Inversion ◽  
Fault Geometry ◽  
Aperture Radar

ABSTRACT Recent earthquakes off the northeastern Kamchatka coast reveal that this region is seismically active, although details of the locations and complexity of the fault system are lacking. The northern part of Kamchatka has poor coverage by permanent seismic stations and ground geodetic instruments. Here, we exploit the Differential Interferometric Synthetic Aperture Radar (DInSAR) technique to characterize the fault geometry and kinematics associated with the 29 March 2017 Mw 6.6 Yuzhno-Ozernovskoe earthquake. The aim is to contribute to identifying the active fault branches and to better understanding the complex tectonic regime in this region using the DInSAR technique, which has never before been applied to the analysis of coseismic offsets in Kamchatka. We produced coseismic deformation maps using Advanced Land Observation Satellite-2 ascending and descending and Sentinel-1A descending Synthetic Aperture Radar (SAR) scenes and detected a predominant uplift up to 20 cm and a westward motion of approximately 7 cm near the shoreline. We jointly inverted the three geodetic datasets using elastic half-space fault modeling to retrieve source geometry and fault kinematics. The best-fit solution for the nonlinear inversion suggests a north–west-dipping oblique reverse fault with right-lateral rupture. The model fault geometry is not only generally consistent with the seismic data but also reveals that a hitherto unknown fault was ruptured. The identified fault structure is interpreted as the northern extension of the east Kamchatka fault zone, implying that the region is more complex than previously thought. Important implications arise for the presence of unknown faults at the edges of subduction zones that can generate earthquakes with magnitudes greater than Mw 6.

scholarly journals Complex rupture process of the 2014 Thailand Mw 6.2 earthquake on the conjugate fault system of the Phayao fault zone

2021 ◽  
Author(s):  
Tira Tadapansawut ◽  
Yagi Yuji ◽  
Ryo Okuwaki ◽  
Shinji Yamashita ◽  
Kousuke Shimizu
Keyword(s):  
Fault Zone ◽  
Fault Plane ◽  
Rupture Process ◽  
Fault System ◽  
Small Scale ◽  
Fault Geometry ◽  
Geological Setting ◽  
Complex Fault ◽  
Finite Fault ◽  
Complex Fault System

The earthquake with a moment magnitude 6.2 that occurred in northern Thailand on 5 May 2014 is the largest recorded in Thailand by modern seismographs; the source is located in the multi-segmented complex fault system of the Phayao fault zone in the northern Thai province of Chiang Rai. This geological setting is appropriate environment for investigating a compound rupture process associated with a geometrically complex fault system in a magnitude-6-class earthquake. To understand in detail the rupture process of the 2014 Thailand earthquake, we elaborate the flexible finite-fault inversion method, used it to invert the globally-observed teleseismic P waveforms, and resolved for the spatiotemporal distribution of both the slip and the fault geometry. The complex rupture process consists of two distinct coseismic slip episodes that evolved along two discontinuous fault planes; these planes coincide with the lineations of the aftershock distribution. The first episode originated at the hypocenter and the rupture propagated south along the north-northeast to south-southwest fault plane. The second episode was triggered at around 5 km north from the epicenter and the rupture propagated along the east-northeast to west-southwest fault plane and terminated at the west end of the source area at 4.5 s hypocentral time. The fault system derived from our finite-fault model suggests geometric complexities including bends. The derived spatiotemporal orientation of the principal stress axis shows different lineations within the two rupture areas and heterogeneity at their edges. This geological setting may have caused the perturbation of the rupture propagation and the triggering of the distinct rupture episodes. Our source model of the 2014 Thailand earthquake suggests that even in the case of small-scale earthquakes, the rupture evolution can be complex when the underlying fault geometry is multiplex.

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