Trending Thrust Faults Research Articles

Near-surface structural model for deformation associated with the February 7, 1812, New Madrid, Missouri, earthquake

The February 7, 1812, New Madrid, Missouri, earthquake (M [moment magnitude] 8) was the third and final large-magnitude event to rock the northern Mississippi Embayment during the winter of 1811–1812. Although ground shaking was so strong that it rang church bells, stopped clocks, buckled pavement, and rocked buildings up and down the eastern seaboard, little coseismic surface deformation exists today in the New Madrid area. The fault(s) that ruptured during this event have remained enigmatic. We have integrated geomorphic data documenting differential surficial deformation (supplemented by historical accounts of surficial deformation and earthquake-induced Mississippi River waterfalls and rapids) with the interpretation of existing and recently acquired seismic reflection data, to develop a tectonic model of the near-surface structures in the New Madrid, Missouri, area. This model consists of two primary components: a north-northwest–trending thrust fault and a series of northeast-trending, strike-slip, tear faults. We conclude that the Reelfoot fault is a thrust fault that is at least 30 km long. We also infer that tear faults in the near surface partitioned the hanging wall into subparallel blocks that have undergone differential displacement during episodes of faulting. The northeast-trending tear faults bound an area documented to have been uplifted at least 0.5 m during the February 7, 1812, earthquake. These faults also appear to bound changes in the surface density of epicenters that are within the modern seismicity, which is occurring in the stepover zone of the left-stepping right-lateral strike-slip fault system of the modern New Madrid seismic zone.

Regional gas geochemistry in an active tectonic zone, Erzurum Basin, eastern Turkey

Abstract The Karasu Plain is an intermontane sedimentary basin with a Miocene—Quaternary volcanicbasement, andesitic-basalticlava flows and fissure eruptions of basaltic lava. It was filled in the early Quaternary by lacustrine fan-delta deposits, and later by fluvial-alluvial fan deposits. The basin is characterized by NNE-SSW trending sinistral wrench faults on its eastern margin and ENE-WSW trending reverse faults on its southern margin. Both systems of active faults intersect very near to Erzurum, which is considered to be the most likely site for the epicentre of a probable future large earthquake. Regional gas geochemistry has therefore been undertaken adjacent to the city of Erzurum, in order to characterize radon levels over the varied lithologies, examine the potential for geological fault mapping and assess the status of fault activity. Initially,41 sites were sampled and analysed for Rn, CO 2 , O 2 and CH 4 in soils along three traverses to the east (8.26km and 4.5km length) and to the west (6.8km length) of Erzurum. During the first investigation, 495 Rn determinations were made from 165 samples at 41 sites over a ten-day period, during which a small earthquake (M=2.95) occurred. Another 211 sites have been subsequently used for Rn investigations including one traverse through the centre of the city. Additionally,water samples were degassed for Rn and soils tested at five key sites around the Erzurum Plain. Radon was readily detected in soils at all sites. Both 222 Rn and 220 Rn were present at most. Soils over major lithologies gave characteristic signals and, in all traverses, anomalously high values coincided with active faults. Little correlation was found between spring gases (thermal and cold) and adjacent soils. De-gassed spring water Rn values proved highest along the southern margin of the basin and CO 2 values were highest along the northern edge.

Salt Dome Growth, Thrust Fault Growth, and Syndeformational Stratigraphy, La Popa Basin Northern Mexico: ABSTRACT

ABSTRACT Surface expression of two salt domes and a thrust fault in the La Popa basin of Northern Mexico near Monterrey, Nuevo Leon suggest a complex history of interrelated salt tectonics, Late Cretaceous clastic and carbonate sedimentation, and thrust fault growth. Detailed stratigraphic analysis of clastic sediments and shallow marine carbonates of the Difunta Group (Campanian and Maestrichtian) near the two salt domes indicate that delta front sandstones thin and pinch out towards the salt domes. Successively higher sandstones lap higher and farther onto the domes and probably covered the domes completely during Late Cretaceous time, though present day erosion precludes the certainty of complete coverage. During high sea level stands, algal and rudistid carbonate banks formed on the flanks of the domes and may also have covered the domes completely. Facies irregularities in the enclosing sedimentary rocks clearly indicate that the salt domes were active during Late Cretaceous time. Though hidden under the allochthonous block of the La Popa fault, a major northwest-southeast trending thrust fault, the presence of a third dome is implied by the occurrence of evaporites on the fault plane and by the presence of similar, though smaller, faults associated with the two exposed domes. The La Papa fault may be thought of as an out-of-the-syncline, southwest verging thrust fault with the overthrust block acting as a trap door for evaporites derived from the salt dome. The largest carbonate bank in the basin, the 250-meter (800-foot) thick La Popa Limestone Lentil, occurs only on the upthrown side of this fault. The downthrown side is comprised of an unusually thick [approximately 4.600-meter (15,000-foot)] sequence of clastic rocks with an atypically high sand/shale ratio. This combination indicates that, during high sea level stands, carbonate banks grew on shoal areas that were present on the overthrust side of the fault. During low sea level stands, deltaic and shallow marine clastic sedimentation became concentrated in low areas associated with the down thrown side of the fault.

Geologic investigations of a “slip gap” in the surficial ruptures of the 1992 Landers earthquake, southern California

A 3‐km‐long gap in the dextral surficial rupture of the 1992Mw= 7.3 Landers earthquake occurs at the north end of a major fault stepover between the Johnson Valley and Homestead Valley faults. This gap is situated along a segment of the Landers rupture that has been modeled geophysically as having a deficit in average slip at depth. To better evaluate the nature of the slip gap, we document in detail the character and distribution of surficial rupture within it. Along the gap, is a northwest trending thrust fault rupture with an average of less than 1 m of northeast directed reverse‐slip and nearly no oblique right slip. We interpret this rupture to be limited to the shallow crust of the northern end of the stepover and to have been the secondary result of dextral shear, rather than a mechanism of rigid‐block slip‐transfer from the Landers‐Kickapoo fault. A zone of en echelon extensional ruptures also occurs along the slip gap, which we interpret as the secondary result of diffuse dextral shear that accommodated less than 0.5 m of west‐northwest extension. These secondary ruptures represent a discontinuity in the surficial dextral rupture of the Landers earthquake, which we propose resulted from the lack of a mature fault connection between the Johnson Valley and Homestead Valley faults. The rupture pattern of the slip gap implies a significant deficit in net surficial slip, which compares favorably with some geophysical models. Aspects of this rupture pattern also suggest a temporal sequence of rupture that compares favorably with geophysical interpretations of the dynamic rupture propagation.

Evidence of vertical and horizontal motions on Venus: Maxwell Montes

Based on full-resolution Magellan radar images, the detailed structural analysis of central Ishtar Terra (Venus) provides new insight to the understanding of the Venusian tectonics. Ishtar Terra, centered on 65° N latitude and 0° E longitude includes a high plateau. Lakshmi Planum, surrounded by highlands, the most important being Maxwell Montes to the East. Structural analysis has been performed with classical remote-sensing methods. Folds and faults identified on radar images were reported on structural map. Their type and distribution allowed to define the style of the crustal deformation and the context in which these structures formed. This analysis shows that Lakshmi Planum formed under a crustal stretching associated with a volcanic activity. This area then became a relatively steady platform, throughout the formation of Maxwell Montes mountain belt. Maxwell Montes is characterized by a series of NNW-SSE trending thrust faults dipping to the East, formed during a WSW-ESE horizontal shortening. In its NW quarter, the mountain belt shows a disturbed deformation controlled by pre-existing grabens and old vertical crustal fault zone. The deformation of this area is characterized by a shortening of cover above a flat detachment zone, with a progressive accommodation to the southwest. All these tectonic structures show evidence of horizontal and vertical crustal movements on Venus, with subsidence, mountain belt raise, West regional overthrusting of this mountain belt, and regional shear zone.

Structure of the Western Rif (Morocco): Possible Hydrocarbon Plays: ABSTRACT

Seismic data offshore and onshore northwestern Morocco (i.e. Atlantic margin, Rharb Basin, Rif foothills) provided a detailed picture of the Western Rif Cordillera. The most external units of the folded-belt consist of allochthonous Cretaceous and Neogene strongly deformed sediments that constitute a westward-directed accretionary wedge. The structure of the accretionary wedge consist of a complex set of thrust and normal faults. The inner part of the study area consist of NW-SE trending thrust faults, partially exposed in the foothills of the Western Rif. Proceeding towards the foreland, thrust faults are offset by low-angle extensional detachments characterized by anastomosing extensional horses. Widespread extension overlying the accretionary wedge defines a Late Neogene episode of extensional collapse. Extension is not characterized by localized conventional half-grabens but consists of a complex extensional system with variable orientation. Locally shale ridges and toe-thrusts characterized by rear extension and frontal compression define a set of mixed extensional-compressional satellite basins that significantly differ from conventional thrust-related piggy-back basins. Satellite basins are filled with Upper Tortonian to Pliocene sediments. Shallow fields of biogenic gas are present in this Upper Neogene succession of the satellite basins. The frontalmost part of the wedge consist of WNW-ESE trending thrust imbricates. A flexuralmore » basin (foredeep) developed as a result of the accretionary prism loading. The foredeep basin discordantly overlies thinn Cretaceous and Lower-Middle Miocene shallow-water sediments that indistinctly cover Plaeozoic basement rocks and Triassic half-grabens. Pre-foredeep units are related to rifting and passive margin development of the Atlantic Ocean. East from the Rharb Basin the Rif Cordillera is essentially unexplored. Few scattered seismic sections display subsurface ramp anticlines similar to those exposed in the mountain belt.« less

Submarine geology and post-opening tectonic movements in the southern region of the Sea of Japan

The submarine geologic structure of the southern region of the Sea of Japan was analyzed on the basis of seismic reflection profile data and bottom samples. The seismic reflection patterns depict sedimentary layers with well-developed onlap and toplap terminations and truncations by submarine erosion. The planes marked by series of onlap, toplap, and erosional truncations enabled us to define three stratigraphic groups composed of six formations in this region. They are the Kasumioki Group, the Hamasakaoki Group and the Tottorioki Group in ascending order. Detailed analysis of the seismic reflection profiles reveals subtle structures of these sedimentary units. The oldest Kasumioki Group is folded and faulted, forming submarine ridges. The Hamasakaoki Group mainly occurs in the depressions between these ridges. The youngest Tottorioki Group covers widely both of the older formations with a pronounced marine onlap. Fossil evidence indicates that the depositional ages of the Kasumioki Group, the Hamasakaoki Group and the Tottorioki Group are Early Miocene to Earliest Pliocene, late Early to Late Pliocene, and Late Pliocene to Holocene, respectively. These observations provide the basis to understand two main structural features in this region; (1) E-W trending folds, and (2) northwestward tilting blocks. The former construct a fold zone composed of two to four ranges of anticlines that have steeper southern flanks truncated by reverse faults. The latter are shown by slightly-inclined floors formed by submarine erosion, step-like asymmetric basins bounded by NE-SW trending reverse faults, and onlap-toplap sedimentation patterns. The lateral change in bed-thickness, sedimentation patterns, and age of submarine sediments indicate that the E-W trending folds were formed in the early Middle or Late Miocene to the Early Pliocene by N-S compression, whereas the northwestward tilt blocks were formed in the late Early to Late Pliocene by NW-SE compression. The sedimentary records in this region dictate an abrupt change in tectonic setting in the late Early Pliocene. This change is interpreted to show that the Sea of Japan has been closing since then due to either the reactivation of the Amurian Plate, or the directional change of the Philippine Sea Plate motion.

Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in northern California: Implications for the development and evolution of a young transform

The northernmost and relatively youthful segment of the San Andreas fault system is situated within a 100+ km wide zone of northwest trending strike‐slip faults that includes, from west to east, the San Andreas, Maacama, and Bartlett Springs faults. Although the San Andreas fault is the principal strike‐slip fault in this system, it has been virtually aseismic since the 1906 earthquake. Moderate levels of seismicity locate to the east along the Maacama fault and, to a lesser extent, the Bartlett Springs fault at focal depths typical of other strike‐slip faults within the San Andreas fault system in central California. North of the San Andreas fault system, within the Cape Mendocino area, earthquakes occur at depths of up to 40 km and primarily reflect internal deformation of the subducting Gorda slab, and slip along the Mendocino Fracture Zone. Seismicity along the Maacama and Bartlett Springs faults is dominated by right‐lateral to oblique‐reverse slip along fault planes that dip 50°–75° to the northeast. The northern extent of seismicity along these faults terminates near the surface projection of the southern edge of the Gorda slab. The onset of seismicity along these faults may be related to the abrupt change in the elastic thickness of the North American plate as it enters the asthenospheric window. The Maacama and Bartlett Springs faults are strike‐parallel with active reverse faults within the forearc region of the Cascadia subduction zone. This preexisting structural fabric of northwest trending reverse faults in the forearc area appears to have strongly influenced the initial slip and complexity of these faults. Continuation of the moderately dipping Maacama fault to the southeast along the steeply dipping Healdsburg and Rodgers Creek fault zones and the near‐vertical Hayward and Calaveras fault zones in the San Francisco Bay area suggests that these faults evolve toward a more vertical dip to minimize the shear stresses that tend to resist plate motion.

Regional Geologic Framework and Petroleum Occurrences

The Falcon Basin developed during the late Eocene as a result of dextral strike slip movement along the Caribbean-South American plate boundary. During the Oligocene and early Miocene as much as 16,000 ft. of sediment, predominantly sandstones and shales, accumulated within the east-west trending pull-apart basin. Localized carbonate buildups were also developing in association with the Paraguana and Dabajuro Platforms. During the middle to late Miocene, uplift of the now emergent Central Falcon Basin Anticlinorium resulted in the northward progradation of delta systems. Sandstones associated with these deltas now make up the producing reservoirs within the basin. The complex present day structural configuration is the result of continued movement along the Caribbean-South American plate boundary. Landsat imagery and field mapping indicate a basin dominated by northeast trending folds and thrust faults and fracture patterns commonly associated with dextral strike-slip movement. Commercial production is currently limited to the Tiguaje and Cumarebo areas. The former occurs as four small fields ([plus minus]52 MMBO) related to structures developed by dextral movement along the Oca fault. The latter Cumarebo Field ([plus minus]60 MMBO) is a thrusted anticline on the northern flank of the Falcon foldbelt. The tectonic complexity and sandstone-dominated nature of the onshoremore » Falcon Basin severely limit potential field size. Significant, yet currently undeveloped, reserves have also been discovered offshore in the Gulf of La Vela. Fractured granite, carbonates and sandstones associated with tilted fault block structures have tested hydrocarbons in several wells.« less

Extent and tectonic significance of the Central Otago shear-strain anomaly

Abstract Recent geodetic crustal strain determinations confirm that a region in Central Otago, New Zealand, is characterised by a principle axis of relative compression with an azimuth lying between 40° and 70°. This region now appears to extend at least as far west as Lake Wakatipu. The northern boundary of this zone lies in the upper Clutha valley, 10 km south of Lake Wanaka. Within the Central Otago region, strain rates increase to the west, with maximum shear-strain rates of 0.6 μrad/yr in the Kawarau area. Strain orientations of 40–70° are difficult to reconcile with the regional tectonic pattern dominated by orthogonal northeast and northwest trending thrust faults, because the azimuth of the principle axis of relative compression is oblique to both sets of faults, which would be consistent with strike-slip rather than dip-slip movement on the faults. A model by which the geodetic strain measurements and the regional tectonics of Central Otago can be reconciled involves simultaneous oblique compress...

UGIJAR AND CANJAYAR NEOGENE BASINS (SE SPAIN): AN EXAMPLE OF STRIKE-SLIP BASIN EVOLUTION IN TRANSPRESSIVE REGIME

The present study has been carried out in the eastern part of the Alpujarran corridor (Betic Chain), an E-W trending basin, 80 km long, of Neogene-Quaternary age. In particular, the Ugijar and Canjayar basins (respectively named Basin 1 and Basin 2), controlled by an E-W trending left stepping right lateral strike­slip system, associated with NE-SW trending thrust faults, have been investigated. The stratigraphic sequence of the forementioned two basins, which can be up to 2000 m thick, is mainly due to tectonic subsidence and is here interpreted in terms of Sequence Stratigraphy. The age of the whole sequence, dated by means of planktonic foraminifera, is Late Serravallian-Pliocene.

MECANISMO DE RIFTEAMENTO DA PORÇÃO OCIDENTAL DA MARGEM NORTE BRASILEIRA, BACIA DO PARÁ-MARANHÃO

The Para-Maranhao basin has been intensely studied during the past year by a special work group created in Petrobras. Its tectonics evolution shows the key processes acting on the Equatorial Margin of Brazil of which it occupies part of its western portion. The basin is bordered to the south by a shallow offshore basement high, the Para-Maranhao Platform, limited at the W by largely E-W trending and at the E by largely NW trending faults. Faults within the basin and bordering inner or external basement lighs (MAS-9, and 1-PAS-19) follow the orientation of faults along the basin margin of the respective (eastern and western) segments. Between the two portions, the NNE trending Gurupi high may mark the NE extremity of a major intracontinental fault; lesser faults trend NNW in the western and NNE in the eastern segment of the basin. The Mesozoic tectonic evolution of the area is proposed to have taken place in four stages. ln Triassic-Jurassic time, contemporaneously with the intrusion of NNW trending basalt dikes along the Amapa margin to the west, the area was submitted to NNW-SSE compression and ENE-WSW extension characteristic of the break-up of Pangea. This compression is increased in early Cretaceous (Neocomian) time by the clockwise rotation of South America as the South Atlantic rift opened. During Alagoas (Aptian) time rifting along the Equatorial Margin reactivated NW-trending strike slipe and E-W trending reverse faults of this compressional phase as normal faults, within NE- trending major strike slipe faults of the compressional phase separate the E and the W portions of the basin. In Albian-Cenomanian time, right lateral movement between NW Africa and Brazil along the early Equatorial fracture zones reactivated the E-W faults as strike slip and the NW trending faults as normal faults, thus enhancing normal faulting and subsidence in the eastern relative to the western portion of the basin, from late Cretaceous time, thermal subsidence dominates.

Structural analysis and interpretation of the surface deformations of the El Asnam Earthquake of October 10, 1980

The El Asnam earthquake of October 10, 1980, represents the major seismotectonic event of these last decades in the West Mediterranean area. It has induced a large amount of surface breaks. This earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of North Africa. The tectonic analysis of surface rupture shows the complexity of the deformation mechanism. The principal mechanism consists of the activation of a NW‐SE trending thrust fault, accompanied with a left‐lateral motion and with an intense deformation of the northwestern overthrusting block. An accurate description of these deformations shows that, for a large part, the breaks geometry depends closely on the substratum structure. Finally, the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation.

Late Quaternary tectonic movements of western and central Asia

Late Pleistocene and Holocene activity on major faults of western and central Asia are inferred from offsets of young topography. Large active strike-slip faults bound the northward-moving Arabian and Indian plates. The Indian plate moves more rapidly with respect to Eurasia than does the Arabian plate, with the highest rate of young lateral motion (1.2 to 1.4 cm/yr) along the Darvaz fault on its northwestern side. Convergence of these plates on the Eurasian plate produces the north-trending compression of the latter. It results in the creation of northwest-trending dextral wrench faults, smaller northeast-trending sinistral faults, east-west–trending thrust faults, and rare north-trending normal and extension faults. The rates of relative motion are slower here than on the borders of the southern plates, being higher to the north of the Indian plate than to the north of the Arabian. Not all relative motion of the southern plates is accommodated by their boundary deformation and by the compression of the Eurasian plate. This motion and resistance of the Eurasian plate produce squeezing of the rock masses on both sides of the southern plates that results in dextral west-trending wrench faulting on the western side and sinistral on the eastern side of each plate. This pattern can be recognized throughout the Neogene-Quaternary tectonic evolution of the Asian segment of the Alpine–central Asian orogenic belt. This paper is an attempt to correlate synchronous tectonic movements over huge areas of the continent. The author believes it is appropriate to recognize in such correlation mobile and stable zones of different scales. The depth and character of motion in the mobile zones define important features of the structure and evolution of the Earth9s crust.

A geological note on the Qir earthquake, SW Iran, April 1972

SummaryThis note outlines some thoughts on the possible significance of the April 1972 Qir earthquake with respect to the geological structure of Fars Province, SW Iran. The area in which the disturbance occurred belongs to a belt of simple folds of the Zagros system. These folds exhibit localized anomalies of structure which are attributed both to renewed movements along deep-seated basement features and to the modifying effects of salt mobility in the subsurface. The absence of surface indications of rupture in the devastated area is puzzling, but the alignment of zones of maximum destruction to buildings suggests a shallow epicentre associated with a concealed N70°W trending thrust fault system. Such seismicity is indicative of the continued activity of the Zagros orogenic movements.