More Like this

1. Constraining the slip rate of the Owl Lake Fault by using LiDAR data and fault scarp degradation models

   https://doi.org/10.32469/10355/94111  

   Altuntas, Gozde; Gomez, Francisco (August 2022, University of Missouri)

   The Owl Lake Fault is an active, 19 to 25-km-long, left-lateral strike-slip fault that divaricates NE from the Garlock Fault toward Death Valley in eastern California and transfers regional strain to the fault systems in Death Valley. As an active fault, the Owl Lake Fault is a poorly understood link between the extension of Death Valley and other active faults within Mojave Desert. In addition to the larger tectonic framework, improved understanding of the Owl Lake Fault as a seismogenic structure has direct implication for the assessment of the earthquake hazard in Eastern California. A significant limitation on the understanding of the Owl Lake Fault's role is the wide range of estimates previously reported for its slip rate. These range from 0.5 to 7.8 mm/yr, which implies the Owl Lake Fault may accommodate nearly all of the present-day slip on the Garlock Fault. The project aims to constrain the slip rate and understand kinematics of the Owl Lake Fault. For this project, I have used recent airborne LiDAR data (approximately 4.6 points/m2) to map the fault and precisely measure horizontally offset landforms along the Owl Lake Fault. Subsequent to LiDAR mapping, field work facilitated the ground-truth verification of initial mapping as well as more precise measurements of small fault offsets using kinematic GPS and low-altitude photogrammetry. The detailed, local microtopography permits assessing the smallest offsets (75-100 cm) which are interpreted as reflecting the last coseismic offset. Initial efforts at refining the slip rate use scarp degradation models to infer the ages of alluvial fans and stream terraces that are offset by faulting. The final step for this project involves estimating slip rate, magnitude, and recurrence interval. Neotectonic investigations allowed to constrain the slip rate of the Owl Lake Fault as 1.1 - 1.4 mm/yr. The Owl Lake Fault can produce earthquake with the magnitude M=7.2 with the 1030 -- 1430-yr recurrence interval. This study demonstrates that the Owl Lake Fault is part of the same hazard consideration as the central Garlock Fault in eastern California. 

   more » « less
2. Geomorphic expression and slip rate of the Fairweather fault, southeast Alaska, and evidence for predecessors of the 1958 rupture

   https://doi.org/10.1130/GES02299.1  

   Witter, Robert C.; Bender, Adrian M.; Scharer, Katherine M.; DuRoss, Christopher B.; Haeussler, Peter J.; Lease, Richard O. (May 2021, Geosphere)

   Abstract Active traces of the southern Fairweather fault were revealed by light detection and ranging (lidar) and show evidence for transpressional deformation between North America and the Yakutat block in southeast Alaska. We map the Holocene geomorphic expression of tectonic deformation along the southern 30 km of the Fairweather fault, which ruptured in the 1958 moment magnitude 7.8 earthquake. Digital maps of surficial geology, geomorphology, and active faults illustrate both strike-slip and dip-slip deformation styles within a 10°–30° double restraining bend where the southern Fairweather fault steps offshore to the Queen Charlotte fault. We measure offset landforms along the fault and calibrate legacy 14C data to reassess the rate of Holocene strike-slip motion (≥49 mm/yr), which corroborates published estimates that place most of the plate boundary motion on the Fairweather fault. Our slip-rate estimates allow a component of oblique-reverse motion to be accommodated by contractional structures west of the Fairweather fault consistent with geodetic block models. Stratigraphic and structural relations in hand-dug excavations across two active fault strands provide an incomplete paleoseismic record including evidence for up to six surface ruptures in the past 5600 years, and at least two to four events in the past 810 years. The incomplete record suggests an earthquake recurrence interval of ≥270 years—much longer than intervals <100 years implied by published slip rates and expected earthquake displacements. Our paleoseismic observations and map of active traces of the southern Fairweather fault illustrate the complexity of transpressional deformation and seismic potential along one of Earth's fastest strike-slip plate boundaries. 

   more » « less
3. Rupture Process of the 2019 Ridgecrest, California Mw 6.4 Foreshock and Mw 7.1 Earthquake Constrained by Seismic and Geodetic Data

   https://doi.org/10.1785/0120200108  

   Wang, Kang; Dreger, Douglas S.; Tinti, Elisa; Bürgmann, Roland; Taira, Taka’aki (July 2020, Bulletin of the Seismological Society of America)

   null (Ed.)

   ABSTRACT The 2019 Ridgecrest earthquake sequence culminated in the largest seismic event in California since the 1999 Mw 7.1 Hector Mine earthquake. Here, we combine geodetic and seismic data to study the rupture process of both the 4 July Mw 6.4 foreshock and the 6 July Mw 7.1 mainshock. The results show that the Mw 6.4 foreshock rupture started on a northwest-striking right-lateral fault, and then continued on a southwest-striking fault with mainly left-lateral slip. Although most moment release during the Mw 6.4 foreshock was along the southwest-striking fault, slip on the northwest-striking fault seems to have played a more important role in triggering the Mw 7.1 mainshock that happened ∼34  hr later. Rupture of the Mw 7.1 mainshock was characterized by dominantly right-lateral slip on a series of overall northwest-striking fault strands, including the one that had already been activated during the nucleation of the Mw 6.4 foreshock. The maximum slip of the 2019 Ridgecrest earthquake was ∼5  m, located at a depth range of 3–8 km near the Mw 7.1 epicenter, corresponding to a shallow slip deficit of ∼20%–30%. Both the foreshock and mainshock had a relatively low-rupture velocity of ∼2  km/s, which is possibly related to the geometric complexity and immaturity of the eastern California shear zone faults. The 2019 Ridgecrest earthquake produced significant stress perturbations on nearby fault networks, especially along the Garlock fault segment immediately southwest of the 2019 Ridgecrest rupture, in which the coulomb stress increase was up to ∼0.5  MPa. Despite the good coverage of both geodetic and seismic observations, published coseismic slip models of the 2019 Ridgecrest earthquake sequence show large variations, which highlight the uncertainty of routinely performed earthquake rupture inversions and their interpretation for underlying rupture processes. 

   more » « less
4. Recency of Faulting and Subsurface Architecture of the San Diego Bay Pull-Apart Basin, California, USA

   https://doi.org/10.3389/feart.2021.641346  

   Singleton, Drake M; Maloney, Jillian M; Brothers, Daniel S; Klotsko, Shannon; Driscoll, Neal W; Rockwell, Thomas K (June 2021, Frontiers in Earth Science)

   In Southern California, plate boundary motion between the North American and Pacific plates is distributed across several sub-parallel fault systems. The offshore faults of the California Continental Borderland (CCB) are thought to accommodate ∼10–15% of the total plate boundary motion, but the exact distribution of slip and the mechanics of slip partitioning remain uncertain. The Newport-Inglewood-Rose Canyon fault is the easternmost fault within the CCB whose southern segment splays out into a complex network of faults beneath San Diego Bay. A pull-apart basin model between the Rose Canyon and the offshore Descanso fault has been used to explain prominent fault orientations and subsidence beneath San Diego Bay; however, this model does not account for faults in the southern portion of the bay or faulting east of the bay. To investigate the characteristics of faulting and stratigraphic architecture beneath San Diego Bay, we combined a suite of reprocessed legacy airgun multi-channel seismic profiles and high-resolution Chirp data, with age and lithology controls from geotechnical boreholes and shallow sub-surface vibracores. This combined dataset is used to create gridded horizon surfaces, fault maps, and perform a kinematic fault analysis. The structure beneath San Diego Bay is dominated by down-to-the-east motion on normal faults that can be separated into two distinct groups. The strikes of these two fault groups can be explained with a double pull-apart basin model for San Diego Bay. In our conceptual model, the western portion of San Diego Bay is controlled by a right-step between the Rose Canyon and Descanso faults, which matches both observations and predictions from laboratory models. The eastern portion of San Diego Bay appears to be controlled by an inferred step-over between the Rose Canyon and San Miguel-Vallecitos faults and displays distinct fault strike orientations, which kinematic analysis indicates should have a significant component of strike-slip partitioning that is not detectable in the seismic data. The potential of a Rose Canyon-San Miguel-Vallecitos fault connection would effectively cut the stepover distance in half and have important implications for the seismic hazard of the San Diego-Tijuana metropolitan area (population ∼3 million people). 

   more » « less
5. Microcontinent Breakup and Links to Possible Plate Boundary Reorganization in the Northern Gulf of California, México

   https://doi.org/10.1029/2021TC006933  

   Higa, Justin T.; Brown, Nathan D.; Moon, Seulgi; Stock, Joann M.; Sabbeth, Leah; Bennett, Scott E. K.; Martín‐Barajas, Arturo; Argueta, Marina O. (January 2022, Tectonics)

   Abstract Faults on microcontinents record the dynamic evolution of plate boundaries. However, most microcontinents are submarine and difficult to study. Here, we show that the southern part of the Isla Ángel de la Guarda (IAG) microcontinent, in the northern Gulf of California rift, is densely faulted by a late Quaternary‐active normal fault zone. To characterize the onshore kinematics of this Almeja fault zone, we integrated remote fault mapping using high‐resolution satellite‐ and drone‐based topography with neotectonic field‐mapping. We produced 13 luminescence ages from sediment deposits offset or impounded by faults to constrain the timing of fault offsets. We found that north‐striking normal faults in the Almeja fault zone continue offshore to the south and likely into the nascent North Salsipuedes basin southwest of IAG. Late Pleistocene and Holocene luminescence ages indicate that the most recent onshore fault activity occurred in the last ∼50 kyr. These observations suggest that the North Salsipuedes basin is kinematically linked with and continues onshore as the active Almeja fault zone. We suggest that fragmentation of the evolving IAG microcontinent may not yet be complete and that the Pacific‐North America plate boundary is either not fully localized onto the Ballenas transform fault and Lower Delfin pull‐apart basin or is in the initial stage of a plate boundary reorganization. 

   more » « less