Neal Driscoll | University of California, San Diego (original) (raw)

Papers by Neal Driscoll

AGUFM, Dec 1, 2007

ABSTRACT

Journal Of Geophysical Research: Solid Earth, Oct 1, 2016

A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, Calif... more A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, California and Mexico, was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting. From the northern Salton Sea to the southern Imperial Valley, the crust is 17-18 km thick and approximately one-dimensional. The transition at depth from Colorado River sediment to underlying crystalline rock is gradual and is not a depositional surface. The crystalline rock from~3 to~8 km depth is interpreted as sediment metamorphosed by high heat flow. Deeper felsic crystalline rock could be stretched preexisting crust or higher-grade metamorphosed sediment. The lower crust below~12 km depth is interpreted to be gabbro emplaced by rift-related magmatic intrusion by underplating. Low upper mantle velocity indicates high temperature and partial melting. Under the Coachella Valley, sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement. Mafic rock does not exist at 12-18 km depth as it does to the south, and a weak reflection suggests Moho at~28 km depth. Structure in adjacent Mexico has slower midcrustal velocity, and rocks with mantle velocity must be much deeper than in the Imperial Valley. Slower velocity and thicker crust in the Coachella and Mexicali valleys define the rift zone between them to be >100 km wide in the direction of plate motion. North American lithosphere in the central Salton Trough has been rifted apart and is being replaced by new crust created by magmatism, sedimentation, and metamorphism. HAN ET AL.

Geology, 2006

Kent et al.'s (2005) article, which claims a 60 k.y. record of extension and slip rates across th... more Kent et al.'s (2005) article, which claims a 60 k.y. record of extension and slip rates across the western boundary of the Basin and Range province, fails to deliver on its promises because of conceptual errors, fl awed procedures, omissions, and other problems. The basic premise of the paper, that shoreline terraces 15 km apart on opposite sides of an extensional basin like Tahoe (CR and RB, Fig. 1) record normal fault slip and slip rates across the basin, is false. It is well known that displacement gradients occur both along and perpendicular to normal faults, with negligible vertical separation 15-20 km into the hanging wall (e.g., Barrientos et al., 1987; Kusznir et al., 1991). Using vertical separation to calculate horizontal components and extension ignores important issues such as oblique slip, transtension, and tilt in half-grabens like Tahoe (Lahren et al., 1999; Schweickert et al., 1999, 2000b). Also, the terrace features themselves are misinterpreted. Kent et al. also fail to address the Tahoe-Sierra frontal fault zone, with its abundant evidence of Quaternary activity, even though this zone forms the true boundary between the Sierra Nevada and the Basin and Range province (Fig. 1; Schweickert et al., 2000a, 2000b, 2004; Howle, 2000). Furthermore, many faults with youthful scarps within the northern part of Lake Tahoe are ignored, and only one fault is assumed to slip in the south half of the lake, implying that faults in the north half of the lake end at their youngest rupture tiplines (Fig. 1). In addition, Kent et al. used fl awed procedures. Large errors may arise from assuming that 14 C ages on charcoal fragments closely date times of lake sedimentation, because charcoal may be sequestered on land for thousands of years before redeposition in the deep lake. The authors also use uncalibrated 14 C ages, whereas calibrated calendar ages may be several thousand years older than the 14 C ages (Stuiver et al., 1998). Other errors arise in comparing heights of terraces using spot elevations, rather than the elevation of the shoreline angle. The authors ignore variations in sedimentation rates, hiatuses, megaturbidites, etc., and extrapolate sedimentation rates at sites CR and NT (Fig. 1) to intervals far beneath and/or far from dated horizons to estimate ages of terraces and the megalandslide. These errors are compounded, making ages too old and slip rates too low. Kent et al. have also mislocated important data points. The piston core and seismic profi le at NT, which are shown as coincident (Kent et al.

Geophysical Research Letters, May 1, 2012

Bulletin of the Seismological Society of America, Apr 1, 2009

High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acqui... more High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acquired in Fallen Leaf Lake (FLL) and Lake Tahoe provide new paleoseismic constraints on the West Tahoe-Dollar Point fault (WTDPF), the westernmost normal fault in the Lake Tahoe Basin, California. Paleoearthquake records along three sections of the WTDPF are investigated to determine the magnitude and recency of coseismic slip. CHIRP profiles image vertically offset and folded strata along the southern and central sections that record deformation associated with the most recent event (MRE) on the WTDPF. Three faults are imaged beneath FLL, and the maximum vertical offset observed across the primary trace of the WTDPF is ∼3:7 m. Coregistered piston cores in FLL recovered sediment and organic material above and below the MRE horizon. Radiocarbon dating of organic material constrained the age of the MRE to be between 3.6 and 4.9 k.y. B.P., with a preferred age of 4.1-4.5 k.y. B.P. In Lake Tahoe near Rubicon Point, approximately 2.0 m of vertical offset is observed across the WTDPF. Based on nearby core data, the timing of this offset occurred between ∼3-10 k:y: B.P., which is consistent with the MRE age in FLL. Offset of Tiogaaged glacial deposits provides a long-term record of vertical deformation on the WTDPF since ∼13-14 k:y: B.P., yielding a slip rate of 0:4-0:8 mm=yr. In summary, the slip rate and earthquake potential along the WTDPF is comparable to the nearby Genoa fault, making it the most active and potentially hazardous fault in the Lake Tahoe Basin.

Geosphere, Jun 17, 2022

The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of t... more The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of the Gulf of California oblique-divergent plate boundary and is also where the southern terminus of the San Andreas fault occurs. Until recently, the distribution of active faults in and around the Salton Sea and their displacement histories were largely unknown. Subbottom CHIRP (compressed high-intensity radar pulse) surveys in the Salton Sea are used to develop a seismic facies model for ancient Lake Cahuilla deposits, a detailed map of submerged active faults, and reconstructed fault displacement histories during the late Holocene. We observe as many as fourteen Lake Cahuilla sequences in the Salton Sea (last ~3 k.y.) and develop a chronostratigraphic framework for the last six sequences (last ~1200 yr) by integrating CHIRP data and cone penetrometer logs with radiocarbon-dated stratigraphy at an onshore paleoseismic site. The Salton Sea contains northern and southern subbasins that appear to be separated by a tectonic hinge zone, and a subsidence signal across hinge-zone faults of 6–9 mm/yr (since ca. A.D. 940) increases toward the south to >15 mm/yr. The faults mapped to the south of the hinge zone appear to accommodate transtension within the San Andreas–Imperial fault stepover. We identify 8–15 distinct growth events across hinge-zone faults, meaning growth occurred at least once every 100 yr since Lake Cahuilla sedimentation began. Several faults offset the top of the most recent Lake Cahuilla highstand deposits, and at least two faults have offset the Salton Sea flood deposits. Active faults and folds were also mapped to a limited extent within the northern subbasin and display growth, but their kinematics and rupture histories require further study. The broad distribution of active faulting suggests that strain between the San Andreas, San Jacinto, and Imperial faults is highly distributed, thus discrepancies between geologic and geodetic slip-rate estimates from these major fault systems are to be expected.

AGU Fall Meeting Abstracts, Dec 1, 2013

Seismic refraction and reflection travel times from the Salton Seismic Imaging Project (SSIP) are... more Seismic refraction and reflection travel times from the Salton Seismic Imaging Project (SSIP) are being used to constrain crustal structure during active continental rifting in the Salton Trough in southern Cal and across the Salton Trough in 2011 Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas Fault system. Seven onshore, two lines and a grid of onshore-offshore data were recorded participated in the field work. First arrival travel time tomography Trough. Crystalline basement in the valley, but shallows to 2 geothermal field. The sediment strong seismic refractor. However, this boundary must be gradational Crystalline basement is interpreted by the high heat flow and hydrothermal activity geothermal field where the heat flow modeling of deeper seismic reflections and a very shallow (~18 km) Moho Seismic Zone, volcanoes and partitioning of strain during continental breakup

2015 AGU Fall Meeting, Dec 17, 2015

AGU Fall Meeting Abstracts, Dec 1, 2015

AGU Fall Meeting Abstracts, Dec 1, 2001

The pattern of differential strain across two major fault strands within the Lake Tahoe basin has... more The pattern of differential strain across two major fault strands within the Lake Tahoe basin has been mapped using a novel combination of high resolution seismic CHIRP, multibeam swath bathymetry, and airborne laser altimetry. Identification of submerged paleo-shorelines of late Pleistocene to early Holocene age allows this past excursion of lake-level to be used as a strain marker to evaluate

AGU Fall Meeting Abstracts, Dec 1, 2012

Faulting in the Inner California Borderlands is complex. In the past, this region has undergone v... more Faulting in the Inner California Borderlands is complex. In the past, this region has undergone various deformational events such as extensional and rotational deformation and variable strike-slip deformation; this has imparted the geomorphology and fault structures observed offshore Southern California. Several hypotheses have been proposed to explain the current fault structures and the hazards they pose to populated coastal regions. The geometry and architecture of these structures can have significant implications for ground motions in the event of a rupture, and therefore impact working models of hazard assessment. Here, focusing on the Newport-Inglewood/Rose Canyon (NI/RC) and Palos Verdes (PV) fault zones, we use new and existing multibeam, CHIRP and Multi-Channel Seismic (MCS) data to describe the geometry of the fault system. We interpret reprocessed (prestack time migration) MCS data collected in 1979, 1986, and 2006 as well as newly acquired high-res MCS datasets collecte...

The Salton Seismic Imaging Project (SSIP) is a collaborative effort between academia and the U.S.... more The Salton Seismic Imaging Project (SSIP) is a collaborative effort between academia and the U.S. Geological Survey to provide detailed, subsurface 3-D images of the Salton Trough of southern California and northern Mexico. From both active- and passive-source seismic data that were acquired both onshore and offshore (Salton Sea), the resulting images will provide insights into earthquake hazards, rift processes, and rift-transform interaction at the southern end of the San Andreas Fault system. The southernmost San Andreas Fault (SAF) is considered to be at high-risk of producing a large damaging earthquake, yet the structure of this and other regional faults and that of adjacent sedimentary basins is not currently well understood. Seismic data were acquired from 2 to 18 March 2011. One hundred and twenty-six borehole explosions (10-1400 kg yield) were detonated along seven profiles in the Salton Trough region, extending from area of Palm Springs, California, to the southwestern ti...

Mass-Transport Deposits in Deepwater Settings, 2011

The pattern of differential strain across two major fault strands within the Lake Tahoe basin has... more The pattern of differential strain across two major fault strands within the Lake Tahoe basin has been mapped using a novel combination of high resolution seismic CHIRP, multibeam swath bathymetry, and airborne laser altimetry. Identification of submerged paleo-shorelines of late Pleistocene to early Holocene age allows this past excursion of lake-level to be used as a strain marker to evaluate

The shallow fault structure of the Incline Village fault, Lake Tahoe NV, has been mapped using a ... more The shallow fault structure of the Incline Village fault, Lake Tahoe NV, has been mapped using a combination of sub-meter resolution seismic CHIRP profiling, conventional paleo-seismic trenching on-shore, and shallow remotely operated vehicle (ROV) imagery. The pairing of these geophysical and geologic techniques has provided new insights into the fault history of the active Incline Village fault. These data, combined

Deformational strain within the Lake Tahoe Basin was mapped during previous campaigns using a com... more Deformational strain within the Lake Tahoe Basin was mapped during previous campaigns using a combination of high resolution seismic CHIRP, multi-beam swath bathymetry, and airborne laser altimetry. These previous campaigns identified submerged paleo-shorelines of Pleistocene to early Holocene age, which act as a tectonic strain marker due to fault related disruptions of this once flat surface, as well as significantly

AGUFM, Dec 1, 2007

ABSTRACT

Journal Of Geophysical Research: Solid Earth, Oct 1, 2016

A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, Calif... more A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, California and Mexico, was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting. From the northern Salton Sea to the southern Imperial Valley, the crust is 17-18 km thick and approximately one-dimensional. The transition at depth from Colorado River sediment to underlying crystalline rock is gradual and is not a depositional surface. The crystalline rock from~3 to~8 km depth is interpreted as sediment metamorphosed by high heat flow. Deeper felsic crystalline rock could be stretched preexisting crust or higher-grade metamorphosed sediment. The lower crust below~12 km depth is interpreted to be gabbro emplaced by rift-related magmatic intrusion by underplating. Low upper mantle velocity indicates high temperature and partial melting. Under the Coachella Valley, sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement. Mafic rock does not exist at 12-18 km depth as it does to the south, and a weak reflection suggests Moho at~28 km depth. Structure in adjacent Mexico has slower midcrustal velocity, and rocks with mantle velocity must be much deeper than in the Imperial Valley. Slower velocity and thicker crust in the Coachella and Mexicali valleys define the rift zone between them to be >100 km wide in the direction of plate motion. North American lithosphere in the central Salton Trough has been rifted apart and is being replaced by new crust created by magmatism, sedimentation, and metamorphism. HAN ET AL.

Geology, 2006

Kent et al.'s (2005) article, which claims a 60 k.y. record of extension and slip rates across th... more Kent et al.'s (2005) article, which claims a 60 k.y. record of extension and slip rates across the western boundary of the Basin and Range province, fails to deliver on its promises because of conceptual errors, fl awed procedures, omissions, and other problems. The basic premise of the paper, that shoreline terraces 15 km apart on opposite sides of an extensional basin like Tahoe (CR and RB, Fig. 1) record normal fault slip and slip rates across the basin, is false. It is well known that displacement gradients occur both along and perpendicular to normal faults, with negligible vertical separation 15-20 km into the hanging wall (e.g., Barrientos et al., 1987; Kusznir et al., 1991). Using vertical separation to calculate horizontal components and extension ignores important issues such as oblique slip, transtension, and tilt in half-grabens like Tahoe (Lahren et al., 1999; Schweickert et al., 1999, 2000b). Also, the terrace features themselves are misinterpreted. Kent et al. also fail to address the Tahoe-Sierra frontal fault zone, with its abundant evidence of Quaternary activity, even though this zone forms the true boundary between the Sierra Nevada and the Basin and Range province (Fig. 1; Schweickert et al., 2000a, 2000b, 2004; Howle, 2000). Furthermore, many faults with youthful scarps within the northern part of Lake Tahoe are ignored, and only one fault is assumed to slip in the south half of the lake, implying that faults in the north half of the lake end at their youngest rupture tiplines (Fig. 1). In addition, Kent et al. used fl awed procedures. Large errors may arise from assuming that 14 C ages on charcoal fragments closely date times of lake sedimentation, because charcoal may be sequestered on land for thousands of years before redeposition in the deep lake. The authors also use uncalibrated 14 C ages, whereas calibrated calendar ages may be several thousand years older than the 14 C ages (Stuiver et al., 1998). Other errors arise in comparing heights of terraces using spot elevations, rather than the elevation of the shoreline angle. The authors ignore variations in sedimentation rates, hiatuses, megaturbidites, etc., and extrapolate sedimentation rates at sites CR and NT (Fig. 1) to intervals far beneath and/or far from dated horizons to estimate ages of terraces and the megalandslide. These errors are compounded, making ages too old and slip rates too low. Kent et al. have also mislocated important data points. The piston core and seismic profi le at NT, which are shown as coincident (Kent et al.

Geophysical Research Letters, May 1, 2012

Bulletin of the Seismological Society of America, Apr 1, 2009

High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acqui... more High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acquired in Fallen Leaf Lake (FLL) and Lake Tahoe provide new paleoseismic constraints on the West Tahoe-Dollar Point fault (WTDPF), the westernmost normal fault in the Lake Tahoe Basin, California. Paleoearthquake records along three sections of the WTDPF are investigated to determine the magnitude and recency of coseismic slip. CHIRP profiles image vertically offset and folded strata along the southern and central sections that record deformation associated with the most recent event (MRE) on the WTDPF. Three faults are imaged beneath FLL, and the maximum vertical offset observed across the primary trace of the WTDPF is ∼3:7 m. Coregistered piston cores in FLL recovered sediment and organic material above and below the MRE horizon. Radiocarbon dating of organic material constrained the age of the MRE to be between 3.6 and 4.9 k.y. B.P., with a preferred age of 4.1-4.5 k.y. B.P. In Lake Tahoe near Rubicon Point, approximately 2.0 m of vertical offset is observed across the WTDPF. Based on nearby core data, the timing of this offset occurred between ∼3-10 k:y: B.P., which is consistent with the MRE age in FLL. Offset of Tiogaaged glacial deposits provides a long-term record of vertical deformation on the WTDPF since ∼13-14 k:y: B.P., yielding a slip rate of 0:4-0:8 mm=yr. In summary, the slip rate and earthquake potential along the WTDPF is comparable to the nearby Genoa fault, making it the most active and potentially hazardous fault in the Lake Tahoe Basin.

Geosphere, Jun 17, 2022

The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of t... more The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of the Gulf of California oblique-divergent plate boundary and is also where the southern terminus of the San Andreas fault occurs. Until recently, the distribution of active faults in and around the Salton Sea and their displacement histories were largely unknown. Subbottom CHIRP (compressed high-intensity radar pulse) surveys in the Salton Sea are used to develop a seismic facies model for ancient Lake Cahuilla deposits, a detailed map of submerged active faults, and reconstructed fault displacement histories during the late Holocene. We observe as many as fourteen Lake Cahuilla sequences in the Salton Sea (last ~3 k.y.) and develop a chronostratigraphic framework for the last six sequences (last ~1200 yr) by integrating CHIRP data and cone penetrometer logs with radiocarbon-dated stratigraphy at an onshore paleoseismic site. The Salton Sea contains northern and southern subbasins that appear to be separated by a tectonic hinge zone, and a subsidence signal across hinge-zone faults of 6–9 mm/yr (since ca. A.D. 940) increases toward the south to >15 mm/yr. The faults mapped to the south of the hinge zone appear to accommodate transtension within the San Andreas–Imperial fault stepover. We identify 8–15 distinct growth events across hinge-zone faults, meaning growth occurred at least once every 100 yr since Lake Cahuilla sedimentation began. Several faults offset the top of the most recent Lake Cahuilla highstand deposits, and at least two faults have offset the Salton Sea flood deposits. Active faults and folds were also mapped to a limited extent within the northern subbasin and display growth, but their kinematics and rupture histories require further study. The broad distribution of active faulting suggests that strain between the San Andreas, San Jacinto, and Imperial faults is highly distributed, thus discrepancies between geologic and geodetic slip-rate estimates from these major fault systems are to be expected.

AGU Fall Meeting Abstracts, Dec 1, 2013

Seismic refraction and reflection travel times from the Salton Seismic Imaging Project (SSIP) are... more Seismic refraction and reflection travel times from the Salton Seismic Imaging Project (SSIP) are being used to constrain crustal structure during active continental rifting in the Salton Trough in southern Cal and across the Salton Trough in 2011 Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas Fault system. Seven onshore, two lines and a grid of onshore-offshore data were recorded participated in the field work. First arrival travel time tomography Trough. Crystalline basement in the valley, but shallows to 2 geothermal field. The sediment strong seismic refractor. However, this boundary must be gradational Crystalline basement is interpreted by the high heat flow and hydrothermal activity geothermal field where the heat flow modeling of deeper seismic reflections and a very shallow (~18 km) Moho Seismic Zone, volcanoes and partitioning of strain during continental breakup

2015 AGU Fall Meeting, Dec 17, 2015

AGU Fall Meeting Abstracts, Dec 1, 2015

AGU Fall Meeting Abstracts, Dec 1, 2001

The pattern of differential strain across two major fault strands within the Lake Tahoe basin has... more The pattern of differential strain across two major fault strands within the Lake Tahoe basin has been mapped using a novel combination of high resolution seismic CHIRP, multibeam swath bathymetry, and airborne laser altimetry. Identification of submerged paleo-shorelines of late Pleistocene to early Holocene age allows this past excursion of lake-level to be used as a strain marker to evaluate

AGU Fall Meeting Abstracts, Dec 1, 2012

Faulting in the Inner California Borderlands is complex. In the past, this region has undergone v... more Faulting in the Inner California Borderlands is complex. In the past, this region has undergone various deformational events such as extensional and rotational deformation and variable strike-slip deformation; this has imparted the geomorphology and fault structures observed offshore Southern California. Several hypotheses have been proposed to explain the current fault structures and the hazards they pose to populated coastal regions. The geometry and architecture of these structures can have significant implications for ground motions in the event of a rupture, and therefore impact working models of hazard assessment. Here, focusing on the Newport-Inglewood/Rose Canyon (NI/RC) and Palos Verdes (PV) fault zones, we use new and existing multibeam, CHIRP and Multi-Channel Seismic (MCS) data to describe the geometry of the fault system. We interpret reprocessed (prestack time migration) MCS data collected in 1979, 1986, and 2006 as well as newly acquired high-res MCS datasets collecte...

The Salton Seismic Imaging Project (SSIP) is a collaborative effort between academia and the U.S.... more The Salton Seismic Imaging Project (SSIP) is a collaborative effort between academia and the U.S. Geological Survey to provide detailed, subsurface 3-D images of the Salton Trough of southern California and northern Mexico. From both active- and passive-source seismic data that were acquired both onshore and offshore (Salton Sea), the resulting images will provide insights into earthquake hazards, rift processes, and rift-transform interaction at the southern end of the San Andreas Fault system. The southernmost San Andreas Fault (SAF) is considered to be at high-risk of producing a large damaging earthquake, yet the structure of this and other regional faults and that of adjacent sedimentary basins is not currently well understood. Seismic data were acquired from 2 to 18 March 2011. One hundred and twenty-six borehole explosions (10-1400 kg yield) were detonated along seven profiles in the Salton Trough region, extending from area of Palm Springs, California, to the southwestern ti...

Mass-Transport Deposits in Deepwater Settings, 2011

The pattern of differential strain across two major fault strands within the Lake Tahoe basin has... more The pattern of differential strain across two major fault strands within the Lake Tahoe basin has been mapped using a novel combination of high resolution seismic CHIRP, multibeam swath bathymetry, and airborne laser altimetry. Identification of submerged paleo-shorelines of late Pleistocene to early Holocene age allows this past excursion of lake-level to be used as a strain marker to evaluate

The shallow fault structure of the Incline Village fault, Lake Tahoe NV, has been mapped using a ... more The shallow fault structure of the Incline Village fault, Lake Tahoe NV, has been mapped using a combination of sub-meter resolution seismic CHIRP profiling, conventional paleo-seismic trenching on-shore, and shallow remotely operated vehicle (ROV) imagery. The pairing of these geophysical and geologic techniques has provided new insights into the fault history of the active Incline Village fault. These data, combined

Deformational strain within the Lake Tahoe Basin was mapped during previous campaigns using a com... more Deformational strain within the Lake Tahoe Basin was mapped during previous campaigns using a combination of high resolution seismic CHIRP, multi-beam swath bathymetry, and airborne laser altimetry. These previous campaigns identified submerged paleo-shorelines of Pleistocene to early Holocene age, which act as a tectonic strain marker due to fault related disruptions of this once flat surface, as well as significantly

The southern San Andreas fault (SSAF) accommodates a significant amount of strain between the Pac... more The southern San Andreas fault (SSAF) accommodates a significant amount of strain between the Pacific and North American plates; thus, the fault represents a major geohazard to the populated areas of southern California, in particular the larger Los Angeles metropolitan area. Paleoseismic chronology of ruptures along the SSAF segment suggests this fault is near the end of its interseismic period (∼180 years), because it has not ruptured in historic times (∼320 years). A recent active-source seismic experiment performed in the Salton Sea west of the SSAF provides evidence for extensional deformation along the northeastern shore of the Salton Sea. This study pos-its that the extensional deformation is due to a previously unmapped fault, here named the Salton trough fault (STF). The seismic reflection data image a divergent sediment package that dips toward the northeast with thicknesses up to at least 2 km. Refraction inversion produces a southwestward-dipping velocity discontinuity that crops out east of the SSAF surface trace, consistent with the existence of a southwest to northeast gradient in lithology. If present, the existence of the STF has scientific and societal relevance. First, the STF appears to control the recent Salton trough architecture north of Bombay Beach. Second, from a seismological hazards perspective, the presence of this structure could alter the current understanding of stress transfer and rupture dynamics in the region , as well as community fault models and ground-motion simulations on the SSAF.