Evidence For Strike-slip Faulting Research Articles

Uncovering Ganymede's past: Tectonics at Nippur/Philus Sulci

Observations of Jupiter's largest moon Ganymede by Voyager and Galileo revealed fractures and evidence of strike-slip faulting, leading to studies for the mechanisms of these structures focused on extensional tectonism and gravitational tidal stresses. In this analysis, we investigate the geologic history of Ganymede in the area of Nippur/Philus Sulci (175°E, 36.9°N) by examining Galileo high-resolution data available for this region (∼100 m/pixel) and conducting a tidal stress investigation of Ganymede's past. Several crosscutting bands of light terrain in the Nippur/Philus Sulci site show varying degrees of tectonic deformation, ranging from smooth and less distorted bands to highly grooved and deformed terrain. The chronology of tectonic activity implied by mapped crosscutting relationships reveals three eras of distinct geologic activity: 1. Ancient, 2. Intermediate and 3. Youngest. Indicators of shear deformation are found throughout all ages of terrain, but mapped early-stage indicators of strike-slip features are exclusively located in intermediate and youngest terrain. An investigated offset feature in intermediate-aged terrain corresponds in slip direction to the predictions from modeling stresses of a higher past eccentricity. However, the en echelon structures found in a younger geologic unit do not align in slip direction with typical first-order R Riedel shears. This suggests that these features might have formed through another process and the observed en echelon folds could be passive structures, which can be created through relatively rapid large displacement on a fault. Through modeling of Ganymede's past tidal stresses, we can conclude that a past higher eccentricity (e > 0.02) could have distorted the Nippur/Philus Sulci region in its second, intermediate phase of main deformation, yielding a stress field conducive to shear failure of the icy upper crust. New data from NASA's Juno mission, as well as future observations by ESA's Jupiter Icy Moons Explorer (JUICE) mission and NASA's Europa Clipper mission, will further aid our understanding of the tectonic history of Ganymede and improve the resolution of tectonic feature analysis.

Strike-slip faulting in the central part of the Sanandaj-Sirjan Zone, Zagros Orogen, Iran

The Sanandaj-Sirjan Zone (SSZ) is one of the main basement tectonic blocks located close to the northeastern margin of the Zagros Orogenic Belt. New observations in the central part of the zone indicate that the fault pattern is dominated by NW-trending longitudinal faults. The components of movement on the fault planes are interpreted as dextral oblique thrusting and dextral strike-slip. The identified structures along the faults were associated with the strike-slip faults (e.g., Hasan-Robat and Najafabad dextral restraining stepovers) and rotated tectonic blocks (arranged in a ‘domino’ configuration) near to the Foladshahr and Kolah-Ghazi mountains. Along the longitudinal faults, the dextral offsets of the rock units, streams, alluvial deposits and rivers were measured. The dextral offset values range from 2.4 to 2.7 km, while the estimated offsets based on the geomorphological features are between 50 and 61 m for streams, up to approximately ∼50 m for alluvial deposits and up to 2.2 km for rivers. The dextral strike-slip component on the fault planes occurs along the northern and southern margins of the SSZ, as well as directly within the zone, west and east of the study area. The evidence for strike-slip faulting in the internal part of the zone suggests that the central part of the SSZ probably was horizontally sheared in a manner consistent with a simple shear ‘card-deck model’.

Using Small, Temporary Seismic Networks for Investigating Tectonic Deformation: Brittle Deformation and Evidence for Strike-Slip Faulting in Bhutan

SUMMARY We processed data from a small, five-station temporary seismic network deployed from January 2002 until March 2003 within the Kingdom of Bhutan. We detected, associated, and located approximately 2,100 teleseismic, regional, and local events; approximately 900 were not in the United States Geological Survey (USGS) Earthquake Data Report catalog. We supple mented our data for these 900 events with data from the Global Seismographic Network (GSN) stations in the region. After relocation of these events, we focused on approximately 175 events that occurred near or within the borders of Bhutan. We reviewed each solution, manually timing the P- and S-waves for each event, and inverted for event locations and an average 1-D velocity model for the region. Our model was tested with other models appropriate for the region. We found a high amount of microseismicity throughout southern Bhutan and almost no seismicity under northern Bhutan and southern Tibet. Our results showed that analysis of data from small in-country seismic networks resulted in new scientific findings. In this case, we found the crust under southern Bhutan brittlely deforming, and there was evidence for strike-slip faulting, supporting previous results for the region.

Neotectonic structures in the area offshore of Alaçatı, Doğanbey and Kuşadası (western Turkey): evidence of strike-slip faulting in the Aegean extensional province

About 400 km of new seismic reflection data has been acquired in the study region offshore of Alaçatı, Doğanbey, and Kuşadası, which enables investigation of the active crustal deformation in this region. The deformation onshore in western Turkey is dominated by crustal extension, and clear evidence of this process is also now available from this offshore area. However, in the onshore area adjacent to this study region evidence of active right-lateral strike-slip faulting has also previously been observed. This strike-slip faulting has previously been thought only to accommodate variations in extension between adjacent normal faults. However, in the offshore area there is considerable evidence of zones of deformation, some of which may link to the strike-slip faulting onshore, suggesting that strike-slip faulting may be of greater importance in this region than previously thought.

Evidence for Strike-Slip Faulting in the Smackover Formation of Northeast Texas and South Arkansas and Its Geological Implications

ABSTRACT Surface expression, seismic profiles, gravity and magnetic mapping, and well control provide evidence for strike-slip faulting in the Smackover Formation of East Texas and South Arkansas. The faulting that occurred after the deposition of Smackover and during the deposition of Buckner Anhydrite appears to be an extension of the South Florida shear zone. Evidence includes drainage patterns; lineaments on Lansat imagery; seismic lines with flower structure fault patterns; magnetic data with ridges broken by right lateral offsets; and well log correlations with abrupt termination of horizons. The strike-slip faulting triggered significant geological events. The faulting breached the mountains and highlands surrounding the ancient Gulf, initiating the drainage systems that subsequently filled the basin. Fault breaks in the Buckner allowed meteoric water to reach the Louann Salt causing dissolution initiating the development of salt basin structure. Early diagenetic events in the Smackover involving fabric selective dissolution and dolomitization also began with the water incursion. Convergent movement along the strike of the fault created basement rock structure. Pre-existing basement structures were truncated and offset. However complex, there is still predictability in the system, the structures will occur along the trace of the fault. Although a strike-slip fault interpretation is a new concept in this region, the option has economic importance, and as more complete subsurface data becomes available, the concept can be tested.

Timing of rifting in the Alboran Sea basin — correlation of borehole (ODP Leg 161 and Andalucia A-1) to seismic reflection data: implications for basin formation

To constrain the timing of rifting in the western, eastern, and northern parts of the Alboran Sea basin, seismic reflectors, corresponding to biostratigraphic boundaries and unconformities from the Miocene to Recent, are correlated using synthetic seismograms. Regions of adjacent coeval compression and extension are found in the Alboran Sea basin. Normal faulting continues in parts of the eastern Alboran Sea basin later than in the western Alboran Sea basin. Seismic reflection data in the vicinity of ODP Site 976 (western Alboran Sea basin) suggest that rifting ended in the Miocene. Near Site 976 (western Alboran Sea basin), no compressional features affect Miocene and younger sediments. In the eastern Alboran Sea basin north of Al-Mansour Seamount (ODP Site 977), normal faults are observed in Miocene and Early Pliocene sediments. Later folds affect Pleistocene-Recent sediments in the eastern Alboran Sea basin (Site 977). After the folding event, there is evidence for normal faulting in Pleistocene-Recent sediments close to Site 977. South of Al-Mansour Seamount (ODP Site 978), compressional features in the eastern Alboran Sea basin from Miocene to Recent are evidenced by reverse faulting followed by folding. In the northern Alboran Sea basin (Andalucia A-1 well), there is evidence for strike-slip faulting in the Late Miocene that can be related to the Serrata fault system. We envision the development of the Alboran Sea basin through a southeasterly migration of the delaminating continental lithosphere to explain younger extension in the eastern Alboran Sea basin. The rate of the migration of the delamination front is of the range of millimeters-centimeters/year. We see evidence for the migration of the delamination front from Miocene to Recent as tectonic inversion occurs near Site 977. In contradiction to an extensional collapse hypothesis for the formation of the Alboran Sea, rifting did not end in the Late Miocene in the entire Alboran Sea basin. We exclude retreating subduction in a westward direction or a westward continental delamination as a model for Alboran Sea basin development because it would predict younger extension in the western part of the basin.

Small non-overlapping offsets of the East Pacific Rise

High-resolution bathymetric surveys1,2 of the East Pacific Rise (EPR) reveal that in addition to overlapping spreading centres (OSCs), the crest of the EPR is offset tiny amounts by smaller features. Recently, Langmuir et al. have shown that despite their subtle bathymetric expression, these small offsets, bends and kinks of the EPR, collectively termed deviations from axial linearity (devals), represent important petrological and tectonic boundaries. Some devals are small non-overlapping offsets (SNOOs) that offset the EPR axis by up to a few hundred metres. Bathymetric contours near SNOOs are usually disturbed from their axis-parallel trend in ways that we interpret as evidence for strike-slip faulting and volcanism at high angles to the trend of EPR axis. We offer a model for the formation of SNOOs and their associated faults that invokes independent magma supply, stochastic active spreading and limited non-rigid behaviour of the neovolcanic zone.

Evidence for Dominance of Normal Dip-Slip Motion on Segment of Flemington Fault in Newark Basin of New Jersey: ABSTRACT

A fracture study conducted on a series of outcrops along U.S. Route 202, beginning approximately 1.5 km east of the Delaware River and extending eastward for a distance of approximately 1.5 km, provides ample evidence for normal dip-slip faulting and virtually no evidence of strike-slip faulting. The study area is located approximately 1 km south of the Dilt's Corner fault, the southern splay of the Flemington fault, and along a line nearly perpendicular to the axis of a broad, open anticline plunging approximately 10°S, 20°E. This anticline is one of several transverse folds on the hanging-wall side of the Flemington-Dilt's Corner fault system. Measurement of more than 150 small faults revealed fewer than 10 with a significant strike-slip component of motion. Most of the small faults in the area strike northeasterly and dip steeply either to the northwest or to the southeast. Of particular interest are faults that strike N40°E and dip approximately 70° to the northwest or southeast. These faults appear to define a conjugate set, and as such would require ^sgr1 to be nearly vertical, ^sgr2 to be horizontal and trending N40°E, and ^sgr3 to be horizontal and trending S50°E. In 1962, Sanders suggested that in addition to considerable dip-slip displacement, the Flemington fault might have a major right-lateral strike-slip component of motion. Manspeizer used right-lateral strike-slip motion on the Flemington fault as part of his rhomb-graben model for the Newark basin. Recently, Burton and Ratcliffe have suggested that the Flemington fault has both right-lateral and normal components of motion on it. Strike-slip motion, at least on the Dilt's Corner splay of the Flemington fault, is not compatible with the observed field data. End_of_Article - Last_Page 1438------------

Relationship Among Earth Stresses, Pore Pressure, and Drilling Problems Offshore Gulf of Alaska

Relationship Among Earth Stresses, Pore Pressure, and Drilling Problems Pore Pressure, and Drilling Problems Offshore Gulf of Alaska This paper presents an integrated analysis of borehole instability problems in the seismically active Gulf of Alaska. A well-documented instance of borehole collapse from one well is used to calculate horizontal stresses. For Gulf of Alaska, horizontal earth stresses were very, high and appear to have contributed to the occurrence of abnormal pore pressures and borehole instability. Introduction To date, drilling costs in the Gulf of Alaska have been high. Rig costs have exceeded $100,000/D in this hostile offshore environment. High fluid pressures have been encountered at relatively shallow pressures have been encountered at relatively shallow depths and have reached gradients as high as 0.89 psi/ft (20.1 kPa/m). Serious problems with borehole psi/ft (20.1 kPa/m). Serious problems with borehole instability have been encountered. These led to fishing operations and necessitated sidetracking operations in one of the two Shell-operated wells. Failure of the borehole wall by spalling, or sloughing, was indicated by caliper surveys and cuttings size. Penetration rates have been low, averaging less than 10 ft/hr (0.84 mm/s), over most of the footage drilled to date. All these factors, when combined with other operational problems, have resulted in a cast in excess of $1,000 /ft ($3,300/m) drilled.The wells drilled so far (Fig. 1) are near a region of active plate subduction and consequent high earthquake activity (Fig. 2). Normal faults are observed in this region, but only at shallow depths of 3,000 to 7,000 ft (900 to 2100 m). At greater depths, although there is some evidence of strike-slip faulting, thrust faults are the prevalent failure feature. This observed fault pattern suggests that at shallow depths the overburden, or vertical earth stress, is greater than the two horizontal stresses, while at greater depths the overburden is less than one or both of the other two earth stresses. 1 Consequently, the confining pressure (average of the three principal earth stresses) pressure (average of the three principal earth stresses) increases much more rapidly with depth here than in regions such as the Texas and Louisiana gulf coasts where only normal faults are observed and where lateral stresses are less than the overburden to great depth. Thus, sediment compaction may have proceeded quite differently in the Gulf of Alaska proceeded quite differently in the Gulf of Alaska than in the Gulf of Mexico. This may explain why methods that have proved useful in the U.S. gulf coast and other similar basins for predicting and detecting abnormal pressures generally have failed to respond in the expected manner to high pressures in the Gulf of Alaska. The high confining pressures also appear to cause the observed borehole failures; however, these failures allowed us to estimate the magnitude and direction of the previously unknown horizontal earth stresses. Regional Geology and Stress Field In the Gulf of Alaska, the Aleutian Trench is the ocean floor expression of the subduction of the North Pacific Plate beneath the North American Plate. Plate. JPT P. 1477

Tectonic Correlations, Klamath Mountains and Western Sierra Nevada, California

The Klamath Mountains province of northwestern California has long been regarded by geologists as a probable northern continuation of the Sierra Nevada province. Attempts at stratigraphic correlations between the two provinces date back to the turn of the century, but attempts at correlation of tectonic elements have been hindered by a lack of data. Clark (I960) proposed a general correlation of north-striking faults in the Klamath Mountains and in the western Sierra Nevada. High-angle faults of the latter area constitute the Foothills fault system, which Clark believed to be of probable strike-slip origin. Recent studies in the southeastern Klamath Mountains demonstrate that the major faults of that region are thrust faults along which thrust plates have moved relatively westward. The contrast in geometry between subhorizontal to moderately dipping Klamath faults and steeply dipping faults of the Foothills system does not refute correlation of the two but can be explained by an eastward steepening of the Klamath thrusts into faults continuous with those of the western Sierra Nevada. Geologic relationships indicate that the Melones fault of the Foothills fault system extends northward into the eastern Klamath region as the Trinity thrust fault. Correlation of the two faults appears probable on the basis of (1) stratigraphic and structural similarities in their hanging wall blocks, (2) the presence of thick bodies of serpentinized peridotites below the Trinity thrust plate and below the hanging wall of the Melones fault in the northwestern Sierra Nevada, (3) permissive evidence for a Late Jurassic age of the two faults, and (4) a postulated curvilinear trace for the Trinity-Melones fault which is parallel to observed curvilinear structural trends farther west. It is believed that steep minor structures within fault zones of the Foothills system, cited by others as evidence for strike-slip faulting, are not incompatible with an origin for the system by thrust faulting. Three of the four fault-bounded Klamath subprovinces are interpreted as having stratigraphic and structural counterparts in the northwestern Sierra Nevada. The Klamath central metamorphic subprovince is regarded as a thrust slice of Devonian(?) metamorphic rocks, which thins northward and southward and is not present in the Sierran region. Eastward steepening of the proposed Klamath-Sierran thrust faults is related to their increasing proximity to the Sierran synclinorium and to their rooting into its western flank. Formation of the thrusts occurred in the Jurassic during a lengthy interval of profound crustal downbuckling and shortening. Rooting of the thrusts into a crustal zone undergoing contemporaneous subsidence and shortening rules out an origin for them by gravitational tectonics from an orogenic high or by extrusion tectonics from a dilating zone. The geometry of Mesozoic orogenesis in the Klamath-Sierran region, including thrust faulting, can best be explained by the convergence of subcrustal convection cells along the axial zone of the Sierran synclinorium.