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Surface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left-lateral and northeast-striking rupture in the Mw 6.4 foreshock and dominantly right-lateral and northwest-striking rupture in the Mw 7.1 mainshock. We present >650 field-based, surface-displacement observations for these ruptures and synthesize our results into cumulative along-strike displacement distributions. Using these data, we calculate displacement gradients and compare our results with historical strike-slip ruptures in the eastern California shear zone. For the Mw 6.4 rupture, we report 96 displacements measured along 18 km of northeast-striking rupture. Cumulative displacement curves for the rupture yield a mean left-lateral displacement of 0.3–0.5 m and maximum of 0.7–1.6 m. Net mean vertical displacement based on the difference of down-to-the-west (DTW) and down-to-the-east (DTE) displacement curves is close to zero (0.02 m DTW). The Mw 6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the Mw 7.1 rupture. The Mw 7.1 rupture is northwest-striking and 50 km long based on 576 field measurements. Displacement curves indicate a mean right-lateral displacement of 1.2–1.7 m and a maximum of 4.3–7.0 m. Net vertical displacement in the rupture averages 0.3 m DTW. The Mw 7.1 displacement distributions demonstrate that maximum displacement occurred along a 12-km-long portion of the fault near the Mw 7.1 epicenter, releasing 66% of the geologically based seismic moment along 24% of the total rupture length. Using our displacement distributions, we calculate kilometer-scale displacement gradients for the Mw 7.1 rupture. The steepest gradients (∼1–3 m/km) flank the 12-km-long region of maximum displacement. In contrast, gradients for the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes are

How plate-boundary processes control intra-continental deformation is a fundamental question in Earth sciences. Although it is long known that the active India–Asia convergence rate increases eastward, how this boundary condition impacts on active growth of the Himalaya is unclear. To address this issue, we conducted a geologic investigation of the Main Frontal Thrust (MFT), the largest and the most dominant active structure in the Himalayan orogen. Using the age and geometry of uplifted river terraces, we establish a minimum Holocene slip rate of 23±6.2 mm/yr along the decollement of the 10 km wide MFT zone in the far eastern Himalaya. This slip rate is partitioned on three structures: at ∼8.4 mm/yr on the Bhalukpong thrust in the north, at ∼10 mm/yr across the growing Balipara anticline in the middle, and at ∼5 mm/yr on the Nameri thrust in the south. Our estimated minimum total shortening rate is significantly higher than the Holocene slip rate of 9±3 mm/yr for the MFT in the western Himalaya. However, this rate is similar to or potentially greater than the slip rate of 21±1.5 mm/yr for the MFT in the central Himalaya. Our results support an early interpretation that active shortening across the Himalayan orogen is mostly accommodated by slip along the narrow MFT zone and its linked decollement beneath the Himalaya. The eastward increase in the Holocene MFT slip rate requires that the plate-boundary force rather than gravitational spreading is the fundamental control on active growth of the Himalayan orogen.

We investigate the style of active transtensional deformation and characteristics of the landscape along the southern segment of the Karakoram fault system through field mapping, structural analysis, and examination of digital topography (SRTM, ASTER), multi-spectral (ASTER, Landsat 7+), and panchromatic (Corona photography) imagery. Our data suggests that wrench-dominated transtension is occurring within a 90-km-wide zone; simple shear within the zone is accommodated by right-lateral R and P shears as well as left-lateral R′ shears, vertical shortening is accommodated by ∼north-striking extensional shear zones and horizontal shortening is accommodated by ∼east–west-trending transtension-related corrugations. Drainage divides strike at high angles and subparallel to the transtension zone. Those that strike at high angles to the zone can be explained by movement along north-striking extensional fault systems, while the geometry of drainage divides subparallel to the zone are consistent with uplift of corrugations as well as rapid uplift of mountain ranges by normal-right-slip faulting.

The three Himalayan lithologic units, the Lesser Himalayan Sequence, the Greater Himalayan Crystalline complex, and the Tethyan Himalayan Sequence, have a specific structural correlation with the Main Central thrust and South Tibet detachment in the central Himalaya. There, the Main Central thrust places the Greater Himalayan Crystalline complex over the Lesser Himalayan Sequence, and the South Tibet detachment places the Tethyan Himalayan Sequence over the Greater Himalayan Crystallines. Although this division has formed the basis for all Himalayan tectonic models, it fails to explain aspects of the geology of the western Himalaya where the Main Central thrust places the Tethyan Himalayan Sequence directly above the Lesser Himalayan Sequence. Our mapping in NW India shows that this relationship results from southward merging of the Main Central thrust and South Tibet detachment. This finding, in conjunction with observed alternating shear senses on the South Tibet detachment, is inconsistent with the wedge-extrusion and erosion-induced channel-flow models (both require only top-to-the-N motion on the South Tibet detachment) but is consistent with a tectonic-wedging model.