Direct Inversion Method of Fault Slip Analysis to Determine the Orientation of Principal Stresses and Relative Chronology for Tectonic Events in Southwestern White Mountain Region of New Hampshire, USA

The orientation and relative magnitudes of paleo tectonic stresses in the western central region of the White Mountains of New Hampshire is reconstructed using the direct inversion method of fault slip analysis on 1–10-m long fractures exposed on a series of road cuts along Interstate 93, just east of the Hubbard Brook Experimental Forest in North Woodstock, NH, USA. The inversion yields nine stress regimes which identify five tectonic events that impacted the White Mountain region over the last 410 Ma. The inversion method has potential application in basin analysi

Seismotectonics in Northeast India : a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications

In Northeast India, threemajor plates interact along two convergent boundaries: the Himalayas and the Indo–Burma Ranges, which meet at the Assam Syntaxis. To clarify this tectonic interaction and the underlying dynamics, we determine the regional seismotectonic stress from the stress inversion of 285 double couple focal mechanism solutions of earthquakes with an average magnitude of 5. We then compare the reconstructed stress regimes with the available information about geodetically determined relative displacements. North–south compression, in a direction consistent with India–Eurasia convergence, prevails in the whole area from the Eastern Himalayas to the Bengal Basin, through the Shillong–Mikir Massif and the Upper Assam Valley. E–W extension in Tibet is related to this N–S India– Eurasia convergence. Not only does the major N–S compression affect the outer segments of the Indo–Burma Ranges, it also extends into the descending slab of Indian lithosphere below these Iranges, although stresses at depth are controlled by bending of the slab beneath the Q1 Burmese arc. The existence of widespread N–S compression in the Bengal Basin, far away from the Himalayan front, is compatible with the previously proposed convergence between a Shillong– Mikir–Assam Valley block and the Indian craton. E–W compression inside this block supports the hypothesis of a component of eastward extrusion. Stress inversion of focal mechanism solutions in the Indo–Burma Ranges reveals a complex stress pattern. The Burmese arc and its underlying lithosphere experience nearly arcperpendicular extension with ESE–WNW trends in the northernmost, NE-trending segment and ENE–WSW trends in the main N–S arc segment. Such extensional stress, documented from many arcs, is likely a response to pull from and bending of the subducting plate. At the same time, the Indo–Burma Ranges are under compression as a result of oblique convergence between the Sunda and Indian plates. The maximum compressive stress rotates from NE–SW across the inner and northern arc to E–W near the Bengal Basin. This rotation is consistent with the deformation partitioning reflected in the rotation of relative displacement vectors, from a SSW-directed Sunda–Burma motion to aWSW-directed Burma–India motion. As a consequence of this partitioning, the major belt-parallel fault zones show a variety of movements across the main N–S arc segment, from right-lateral slip in the inner ranges to oblique reverse-dextral slip in the outer ranges and pure thrusting in the westernmost foreland belt

Frontal belt curvature and oblique ramp development at an obliquely collided irregular margin : geometry and kinematics of the NW Taiwan fold-thrust belt

Combined structural and tectonic analyses demonstrate that the NW Foothills of the Taiwan collision belt constitute mainly an asymmetric “primary arc” type fold-thrust belt. The arcuate belt developed as a basin-controlled salient in the portion of the foreland basin that was initially thicker, due to the presence of a precollisional depocenter (the Taihsi basin). Additional but limited buttress effects at end points related to interaction with foreland basement highs (Kuanyin and Peikang highs) may have also slightly enhanced curvature. The complex structural pattern results from the interaction between low-angle thrusting related to shallow decollement tectonics and oblique inversion of extensional structures of the margin on the southern edge of the Kuanyin basement high. The tectonic regimes and mechanisms revealed by the pattern of paleostress indicators such as striated outcrop-scale faults are combined with the orientation and geometry of offshore and onshore regional faults in order to accurately define the Quaternary kinematics of the propagating units. The kinematics of this curved range is mainly controlled by distributed transpressional wrenching along the southern edge of the Kuanyin high, leading to the development of a regional-scale oblique ramp, the Kuanyin transfer fault zone, which is conjugate of the NW trending Pakua transfer fault zone north of the Peikang basement high. The divergence between the N120° regional transport direction and the maximum compressive trend that evolved from N120° to N150° (and even to N–S) in the northern part of the arc effectively supports distributed wrench deformation along its northern limb during the Pleistocene. The geometry and kinematics of the western Taiwan Foothills therefore appear to be highly influenced by both the preorogenic structural pattern of the irregularly shaped Chinese passive margin and the obliquity of its Plio-Quaternary collision with the Philippine Sea plate

Frontal belt curvature and oblique ramp development at an obliquely collided irregular margin : geometry and kinematics of the NW Taiwan fold-thrust belt

Combined structural and tectonic analyses demonstrate that the NW Foothills of the Taiwan collision belt constitute mainly an asymmetric “primary arc” type fold-thrust belt. The arcuate belt developed as a basin-controlled salient in the portion of the foreland basin that was initially thicker, due to the presence of a precollisional depocenter (the Taihsi basin). Additional but limited buttress effects at end points related to interaction with foreland basement highs (Kuanyin and Peikang highs) may have also slightly enhanced curvature. The complex structural pattern results from the interaction between low-angle thrusting related to shallow decollement tectonics and oblique inversion of extensional structures of the margin on the southern edge of the Kuanyin basement high. The tectonic regimes and mechanisms revealed by the pattern of paleostress indicators such as striated outcrop-scale faults are combined with the orientation and geometry of offshore and onshore regional faults in order to accurately define the Quaternary kinematics of the propagating units. The kinematics of this curved range is mainly controlled by distributed transpressional wrenching along the southern edge of the Kuanyin high, leading to the development of a regional-scale oblique ramp, the Kuanyin transfer fault zone, which is conjugate of the NW trending Pakua transfer fault zone north of the Peikang basement high. The divergence between the N120° regional transport direction and the maximum compressive trend that evolved from N120° to N150° (and even to N–S) in the northern part of the arc effectively supports distributed wrench deformation along its northern limb during the Pleistocene. The geometry and kinematics of the western Taiwan Foothills therefore appear to be highly influenced by both the preorogenic structural pattern of the irregularly shaped Chinese passive margin and the obliquity of its Plio-Quaternary collision with the Philippine Sea plate