Upper-plate Fault Research Articles

Quaternary deformation along the Wharekauhau fault system, North Island, New Zealand: Implications for an unstable linkage between active strike‐slip and thrust faults

The southern Wairarapa region of the North Island of New Zealand preserves a variably deformed late Quaternary stratigraphic sequence that provides insight into the temporal variability in the partitioning of contraction onto faults in the upper plate of an obliquely convergent margin. Detailed mapping, stratigraphic data, and new radiocarbon and optically stimulated luminescence ages from Quaternary units reveal the interaction between tectonics and sedimentation from ∼125 ka to <9 ka along the Wharekauhau thrust and related faults (i.e., Wharekauhau fault system) at the southern end of the Wairarapa fault zone, a major oblique‐slip fault in the upper plate of the Hikurangi Margin. The Wharekauhau thrust accommodated a minimum of 280 ± 60 m of horizontal shortening from ∼70 to 20 ka. The inferred shortening rate, 3.5–8.4 mm/yr, may have accounted for 11–30% of margin‐normal plate motion. By ∼20 ka, the thrust was abandoned. Subsequent deformation at shallow levels occurred on a segmented fault system that accommodated <1 mm/yr shortening. Active deformation in the region is partitioned between slip on (1) the more western Wairarapa‐Mukamuka fault system (dominantly dextral slip but also causing local uplift of the coast); (2) a series of discontinuously expressed strike‐slip faults and linking blind oblique‐reverse thrusts near the trace of the inactive Wharekauhau thrust; and (3) a blind thrust fault farther to the east. The spatial and temporal complexity of the Wharekauhau fault system and the importance it has had in accommodating upper plate deformation argue for an unsteady linkage between upper plate faults and between these faults and the plate interface.

The 2007 Pisco, Peru, earthquake (M8.0): seismology and geodesy

We investigate the 2007 Pisco, Peru, earthquake (M8.0) using seismological and geodetic data. Analysis of teleseismic records indicates that the earthquake is characterized by a steadily increasing moment rate, with the maximum occurring between about 55 and 70 s and the associated slip occurring about 40 km south of the epicentre. We combine InSAR data from L-band (ALOS) and C-band (Envisat) satellites to produce a 3-D image of the ground displacements caused by the earthquake. Distributed slip inversions of the interferograms identify a single large patch of slip in the location of the maximum moment rate identified by seismology. Despite a clear spatial coincidence between the location of the coseismic slip and the anomalously high topography of the Paracas Peninsula, we find no evidence that the earthquake was directly responsible for motion on any upper plate faults.

Motion on upper‐plate faults during subduction zone earthquakes: Case of the Atacama Fault System, northern Chile

Motion on the Atacama Fault System (AFS) in northern Chile is driven by Andean subduction zone processes. We use two approaches, observational and theoretical, to evaluate how the AFS and other forearc faults responded to coseismic stress induced by one well‐studied megathrust earthquake, the 1995 Mw = 8.1 Antofagasta event. We use synthetic aperture radar interferometry (InSAR) to search for small‐scale coseismic and postseismic deformation on individual faults. The InSAR data are ambiguous: some images show offset consistent with coseismic faulting on the Paposo segment of the AFS and others lack such signal. The fact that we do not observe the fault‐like displacement in all coseismic interferograms suggests that atmospheric contamination, not tectonic deformation, is responsible for the signal. To explore the capacity of the earthquake to trigger motion on upper plate faults, we use seven published slip maps constrained by geodetic and/or seismic data to calculate static and dynamic Coulomb stress change (CSC) on faults in the Antofagasta region. The static CSC field varies between models and depends on the distribution of coseismic interplate slip. On the basis of the CSC distribution predicted by our preferred model constrained by all available data, we suggest it was unlikely that the Antofagasta earthquake directly triggered normal motion on the AFS, and the InSAR data are consistent with this null result. Field reports of normal faulting related to the earthquake may reflect recent (but not coseismic) motion or highly localized behavior not representative of the regional coseismic stress field.

Temporal stability of deformation rates: Comparison of geological and geodetic observations, Hikurangi subduction margin, New Zealand

We examine how well contemporary horizontal velocity fields from Global Positioning System (GPS) geodetic measurements describe long-term deformation rates. Million-year rates of extension, shortening, strike slip and vertical-axis rotations are compared with modelling of GPS velocities from the last 10–15 years in the Hikurangi subduction margin, New Zealand. Within measurement uncertainties of mainly ≤ 50%, the rates of deformation and vertical-axis rotations for each time interval are usually indistinguishable. The comparable deformation rates are consistent with the notion of near-constant rates since ∼ 1.5 Ma. During this time oblique relative plate motion was partitioned, with the majority (85%) of margin-normal motion accommodated on the plate interface, and most (≥ 60%) margin-parallel motion by strike-slip faulting and vertical-axis rotations in the upper plate. Prior to ∼ 1.5 Ma GPS velocities cannot be reliably used to describe deformation and rotations of the Hikurangi margin because, at this time, the Taupo Rift commenced opening, the boundary between Raukumara and Wairoa rotational domains was abandoned and the rates of upper-plate shortening increased. The broad compatibility of GPS and geological deformation and rotation rates since ∼ 1.5 Ma suggests that the build up of contemporary elastic strains in the North Island, measured by GPS, is largely uniform for much of the duration of each seismic cycle. The good agreement between the GPS and geological deformation rates in the North Island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large-magnitude earthquakes.

Multiple sources for late-Holocene tsunamis at Discovery Bay, Washington State, USA

Nine muddy sand beds interrupt a 2500-yr-old sequence of peat deposits beneath a tidal marsh at the head of Discovery Bay on the south shore of the Strait of Juan de Fuca, Washington. An inferred tsunami origin for the sand beds is assessed by means of six criteria. Although all the sand beds contain marine diatoms and almost all the beds display internal stratification, the areal extent of the oldest beds is too limited to confirm their origin as tsunami deposits. The ages of four beds overlap with known late- Holocene tsunamis generated by plate-boundary earthquakes at the Cascadia subduction zone. Diatom assemblages in peat deposits bracketing these four beds do not indicate concurrent change in elevation at Discovery Bay. Diatoms in the peat bracketing a tsunami bed deposited about 1000 cal. yr BP indicate a few decimeters of submergence, suggesting deformation on a nearby upper-plate fault. Other beds may mark tsunamis caused by more distant upper-plate earthquakes or local submarine landslides triggered by earthquake shaking. Tsunamis from both subduction zone and upper-plate sources pose a significant hazard to shoreline areas in this region.

The effects of upper plate deformation on records of prehistoric Cascadia subduction zone earthquakes

Abstract Geophysical data from the offshore Cascadia forearc reveal many Quaternary upper-plate faults and folds. Most active structures are within the accretionary wedge, but significant deformation is also found on the continental shelf. Several faults and synclines project into adjacent coastal bays where deformation of Pleistocene marine terraces is reported. Rapidly buried marsh deposits and drowned forests in these coastal lowlands are interpreted to record coseismic deformation by prehistoric subduction zone earthquakes. The extent and amount of such coastal subsidence has been used to infer characteristic magnitudes and recurrence intervals. However, the record may incorporate both elastic strain release on the subduction zone and localized permanent upper-plate deformation. Movement on upper-plate structures may be triggered by a subduction zone earthquake, as observed in the Nankai and Alaskan forearcs. Alternatively, they may deform independently of subduction zone earthquakes. Regardless of which style of deformation predominates, the record of coseismic subsidence is likely to be affected. Crustal deformation may also contribute to the preservation of subsided marshes. Modelling of subduction zone earthquake characteristics based on coastal marsh stratigraphy is likely to be inaccurate in terms of: (a) total apparent rupture length and earthquake magnitude; (b) amount of subsidence and hence the position of the locked zone; (c) recurrence interval. Most of these shelf and coastal structures respond to N-S compression, in contrast to convergence-related northeasterly compression in the accretionary prism, but in agreement with the regional stress field. Despite low historical coastal and continental shelf seismicity, upper-plate faults may also pose an independent seismic hazard.

Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport

Research Article| March 01, 1999 Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport Kathi K. Beratan Kathi K. Beratan 1Department of Geology and Planetary Science, 321 EH, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kathi K. Beratan 1Department of Geology and Planetary Science, 321 EH, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (3): 259–262. https://doi.org/10.1130/0091-7613(1999)027<0259:MPMWMS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kathi K. Beratan; Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport. Geology 1999;; 27 (3): 259–262. doi: https://doi.org/10.1130/0091-7613(1999)027<0259:MPMWMS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Potassium enrichment within the upper plate of the Whipple detachment fault, southeastern California, occurred as a discrete pulse between 18.5 and 14 Ma, following the most intense extension and prior to the last episode of movement on the detachment fault. This timing is not consistent with a hydrothermal model for K enrichment in which the K is derived from propylitic alteration of lower-plate rocks. Instead, the temporal and spatial distribution of K enrichment supports a diagenetic model in which the K was derived from leaching of Tertiary alkalic volcanic rocks and dissolution of rhyolitic ashes by alkaline-saline brines in a lake and circulating ground water. The most intense alteration is commonly associated with mapped upper-plate faults, although not all mapped faults display evidence of K metasomatism. Fracture porosity present along active faults may have provided a conduit for K-bearing fluids, thus marking a set of faults as coeval and cogenetic. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quaternary upper plate deformation in coastal Oregon

The leading edge of the North American plate along the Cascadia subduction zone is deforming and rotating clockwise as a consequence of both underthrusting of the Gorda- Juan de Fuca plate and collision of the North American plate with the Pacific plate. The details of late Quaternary (≤125 ka) upper-plate deformation resulting from these plate interactions are largely obscured because the most recent deformation overprints earlier deformation in the Tertiary rocks of the Coast Range. However, by mapping uplifted wave-cut platforms formed during times of high sea level in the past ≈500 000 yr, we identify faults and folds active in the late Quaternary in central coastal Oregon. Through a long-coast correlation of these platforms using elevation and soil development, we infer that several major faults have vertically offset platforms at rates as high as 0.6 m/k.y. for the past 125 k.y. We regionally extend our analysis by incorporating all known faults and folds in southern and central coastal Oregon that deform wave-cut platforms. Most platforms along the southern and central Oregon coast have been uplifted at rates of 0.1–0.3 m/k.y. since the late Pleistocene; however, platform uplift rates approach 1 m/k.y. in the vicinity of faults. The trend and distribution of these upper-plate coastal faults are consistent with their interpreted role as left-lateral, strike-slip, block-bounding structures accommodating clockwise rotation. We speculate that these upper-plate faults have a component of dip slip because of their association, in many instances, with localized uplift. If these faults bound rotating blocks, the dip-slip component of displacement may be either contractional or extensional, depending on the orientation of the fault relative to the north-south trend of the plate margin.

Extensional Tectonics of a Part of the Southwestern White Pine Range, Nevada: Implications for Petroleum Occurrence in Railroad Valley: ABSTRACT

Extension exerts controls on migration and trapping of petroleum in rift settings, such as the Great Basin. Extensional controls are critical to the accumulation of petroleum in Nevada, including in Pine and Railroad Valleys. In these fields, reservoir permeability increased due to extension-related fracturing. These fractured reservoirs and structural traps may be contained within upper plates to regional detachments. Just northeast of Nevada`s most productive oil fields, a regionally extensive detachment is exposed in the White Pine Range. This detachment, the Blackrock fault, is a presently low, angle normal fault which dips <30{degrees} along most of its surface trace. The Blackrock fault is nonplanar and exhibits drastic changes in both orientation and geometry along its length. The amount of stratigraphic separation across the fault is also highly variable ranging from <30 to {approximately}3800 m. Upper plate structures to the Blackrock fault may influence oil fields in Railroad Valley. Rocks in the hanging wall of the Blackrock fault are more intensely faulted than rocks in the footwall. The upper plate faults strike north, northwest, east, and northeast. The {approximately}east-striking faults are youngest because they typically cut the other structures. These faults are closely spaced and largely interconnected which allows migration ofmore » hydrocarbons. Most of the hanging wall faults are high-angle normal faults which cut both Paleozoic and Oligocene rocks. In the Blackrock upper plate, Paleozoic, carbonate and minor siliciclastic rocks are unconformably overlain by Oligocene tuffs and tuffaceous sedimentary rocks of the Garret Ranch Group with interbedded rhyolites. Upper plate fracturing of the Paleozoic rocks and Garret Ranch Group is important because parts of both sections are producing reservoirs in Railroad Valley.« less

Stratigraphic and structural synthesis of a Miocene extensional terrane, southeast California and west-central Arizona

Detailed stratigraphy and isotopic dating of stratigraphic sections in the Colorado River extensional corridor support a regional correlation of highly faulted Tertiary stratigraphic sequences and provide a chronologic framework for interpreting the evolution of low-angle normal (detachment) faults. On the basis of this correlation, we define six tilting domains in the upper plate of the Whipple, Chemehuevi, and Rawhide detachment faults and identify three discrete episodes of detachment faulting that began in the early Miocene and ended in middle Miocene time. Episodes of rapid detachment faulting are indicated by extreme tilting of upper-plate fault blocks and overlying Miocene sequences, fanning dips of basinal deposits, and angular unconformities that represent short time gaps in the accumulation of syntectonic sequences. During the first episode of detachment faulting at about 20 Ma, the upper plate segmented to form the domains. Basin subsidence and extreme tilting of upper-plate fault blocks and syntectonic deposits characterized the eastern Topock, Crossman, Aubrey, Parker Dam, and Buckskin-Rawhide domains, whereas the western Mopah domain was the site of abundant volcanic activity but no basins or tilting. A second episode of extension at about 18 Ma produced extreme tilts in the Buckskin-Rawhide domain but upper-plate blocks in the Mopah domain tilted moderately. A third regionwide faulting episode between 14 and 12 Ma was due to localized uplift of middle and lower crust and eventual exposure of the detachment faults and their footwalls. The upper-plate fault blocks responded passively to localized slip on the detachment faults. Rapid extension began on the Whipple-Chemehuevi detachment fault at 20 Ma and had shifted southward to the Buckskin-Rawhide detachment fault by 18 Ma; volcanic activity also shifted southward to the Buckskin-Rawhide domain at this time. The southward shift of rapid extension and volcanism probably represents buildup and release of strain at localized sites in the lower plate. Otherwise, stratigraphic and structural relations indicate that the locations of upper-plate basins, faulting and tilting of upper-plate blocks, and position of the breakaway zone remained stable throughout the major phases of extension.

Tertiary sedimentary rocks associated with the harcuvar core complex in Arizona (U.S.A.): insights into paleogeographic evolution during displacement along a major detachment fault system

Geologic mapping and analysis of Oligocene-Miocene sedimentary rocks in the upper plate of the Buckskin-Rawhide detachment fault system (west-central Arizona) reveals a complex paleogeographic history during fault displacement, involving shifting sediment-source areas and multiple drainage reversals. Within the study area, four upper-plate fault blocks are capped by homoclinal sedimentary sections that display fanning dip relationships indicating concurrent tilting and sedimentation. During deposition of these strata, upper-plate sedimentation was intermittently confined to separate half-graben, while at other times rapid rates of aggradation relative to fault-displacement resulted in burial of ridges separating sub-basins. Four sedimentary assemblages recognized within the study area can be correlated between fault blocks on the basis of lithologic similarity, stratal position, provenance, paleocurrent data, and sparse geochronologic constraints. The basal assemblage consists of lacustrine rocks and interfingering fluvial strata composed of detritus derived from the granitic terrane surrounding the northern part of the study area. These sediments were deposited during the earliest stages of tilting of upper-plate fault blocks, and inferred displacement along the Buckskin—Rawhide detachment fault system. The lower assemblage, which directly overlies the basal assemblage, consists of fine-grained lacustrine deposits, sandy conglomerate and breccia. During lower-assemblage deposition, mass-flow-dominated alluvial fans were derived from source areas consisting mainly of Mesozoic and Paleozoic rocks exposed to the south of the study area. These source areas may have been associated with the breakaway fault of the detachment system, or with fault blocks stranded above structurally elevated parts of the footwall. Tilting of fault blocks continued during deposition of the lower assemblage and strongly affected dispersal patterns and lithofacies distributions; lacustrine sediments were deposited mainly within large, deep sub-basins and, with few exceptions, lower-assemblage streams followed half-graben axes. The middle assemblage consists of conglomerate and sandstone deposited by an extensive south-directed stream system that probably flowed off undistended parts of the hanging wall, across extended parts, and locally onto the footwall. Tilting of upper-plate fault blocks continued during middle-assemblage deposition, but rapid burial of escarpments by sediment permitted relatively unobstructed southward drainage. The upper assemblage consists of sandy conglomerate deposited by a northeast-directed system of broad, shallow streams. These deposits display a variety of clast types, including Tertiary mylonitic, sedimentary, and volcanic rocks that were eroded from the upwarped footwall of the core complex and overlying klippen. Upper-assemblage streams maintained relatively consistent northeasterly flow, even during the early stages of deposition when some fault blocks were still rotating.

Miocene low-angle normal faulting and dike emplacement, Homer Mountain and surrounding areas, southeastern California and southernmost Nevada

Homer Mountain and surrounding regions are within, or adjacent to, the western part of a broad region of low-angle normal faults exposed within the lower Colorado River trough. During middle Miocene time, upper-plate rocks in the Homer, Sacramento, Dead, and Newberry Mountains moved eastward or northeastward, relative to the lower plate, above single or multiple low-angle normal faults. Deposition of coarse clastic sedimentary rocks occurred during extensional faulting and was accompanied by, and closely followed by, eruption of basaltic volcanics. Upper-plate fault blocks of Miocene volcanic and sedimentary rocks and older, underlying crystalline rocks are tilted gently to steeply to the west or southwest. Low-angle normal faults have complex, sinuous traces due to the irregular form of fault surfaces. Antiformal warping and uplift of the lower plate about a north-south trending axis, due to tectonic denudation and isostatic rebound, divided the regionally east-thickening extensional allochthon into separate synformal and wedge-shaped components. The Homer Mountain area lies within, or adjacent to, the synformal component. Lower-plate rocks are intruded by numerous, middle Miocene, east-west-trending dikes, which are in turn intruded by subhorizontal dikes. Both sets of dikes are cut and displaced by low-angle normal faults except on the west flank of the Newberry Mountains where an east-west–trending dike cuts the basal low-angle normal fault. K-Ar geochronologic and field data establish the approximate synchroneity of dike emplacement and low-angle faulting. The state of stress in the lower plate, as inferred from dike orientations, differed radically from the state of stress in the upper plate, as inferred from fault geometry. Low-angle faulting and east-northeast-west-southwest distension of upper-plate rocks reflect regional reduction of compression in the east-northeast-west-southwest direction and associated large-scale east-northeast-west-southwest crustal extension. In contrast, concave-upward flexure of the lower plate, in response to tectonic denudation and resultant isostatic uplift, is inferred to have produced local subhorizontal compression at shallow crustal levels in the lower plate that overwhelmed the regional extensional stress and prevented emplacement of dikes oriented perpendicular to the direction of regional extension. North-south crustal extension during dike emplacement appears to have resulted from minor divergence of lower-plate crustal blocks as they were displaced in a west-southwest direction away from the Colorado Plateau.