Since Death Valley is inside a National Park, it might be very difficult to collect intrusive geophysical data such as seismic reflection and refraction profiles. That would be the best way to see what is going on in the geology beneath the basin sedimentary section.
The current USGS geologic mapping of the park which has been delayed for 20 years due to funding and staffing issues since the early 2000's that is used by NPS internally for management purposes and is currently under renewed preparation for publication by the Geologic Framework of the Intermountain West Project (https://www.usgs.gov/centers/geosciences-and-environmental-change-science-center/science/geologic-framework#overview) strongly suggests exactly the fault you are proposing. There are surface exposures of uncertain Quaternary age offset and lineaments along this trend. Offsets have been identified in alluvium and paleo-spring deposits off the flank of the Cottonwoods south of Dry Bone Canyon and along several mapped strands of faulting on trend outboard of the ne edge of Tucki Mtn. Multiple lineaments are also identified along the western side of Cottonball Basin. This 100k map product has remained unpublished for 2 decades but we hope to have it re-reviewed and published in updated digital format in the next few years. Older regional mapping and sparse gravity data in the park was used to draw some earlier geophysically inferred structures moderately similar to your suggestion (https://pubs.usgs.gov/mf/2002/mf-2381/) but the seismic data absolutely supports the general trend you have drawn as a fault zone with probable late Miocene through younger motion. Faulting on the west side of Mesquite Flat was incorporated into the USGS regional cross sections (https://pubs.usgs.gov/mf/2001/mf-2370/), hydrostructural map (https://pubs.usgs.gov/mf/2002/mf-2372/), and regional groundwater flow model (https://pubs.usgs.gov/pp/1711/) but they were shifted too far west, and I agree with your location based upon my more recent and detailed mapping of the area.
I agree that the earthquake swarm/sequence is probably not on the Towne Pass fault. However, with respect to the text that states "Second, it is not known to be active based on surface geology", readers should be aware of the different uses of the term "active". For California, under the Alquist Priolo Earthquake Fault Zoning Act, "active" faults have moved in the past 11,700 years (Holocene-active) and if zoned by the state, have regulatory requirements for developments within these fault zones. The USGS, classifies the Towne Pass fault as "Late Quaternary active" (as evidenced by some impressive grabens and scarps at the range front), so has the potential to cause large earthquakes and is included as a seismic source in the USGS National Seismic Hazard Model. Regardless of the details, I like the possibility of Option 3 of an unmapped buried strike slip fault, which is consistent with what we have seen so far in this sequence.
Hi Tim, thanks for the comments on the classification of the Towne Pass Fault. I have updated the text with a mention of your comment, so anyone interested can follow up. Cheers - Kyle.
Sounds good to me. I'm always a proponent of unmapped faults. There's no recent scarp, but there is a suspicious NW-aligned row of hills, defining a straight line along their west sides, near the edge of the alluvial fan near there (e.g., 36.6, -117.0816).
As for the Towne Pass Fault, I agree that it's probably not the droid you're looking for, but it sure looks active to me. Maybe just a long recurrence interval? Here's a view from the ground, from my Mojave YouTube series:
Hi Nick, I remember that sequence from your intrepid crossing of Death Valley, because it was one of the few places where your track crossed my personal historical track. I do think a lot of these sub-mm-per-year kinds of faults can have big earthquakes, which means recurrence intervals of many thousands of years for the large events that break the surface.
I did see the row of hills you mention but couldn't convince myself that they were related to young faulting, so I left them out.
Do you have any plans for another epic trek? - Kyle
I agree those hills have no apparent Quaternary fault activity . . . but it's usually easier to reactivate an old fault than to tear a new one, eh? It'll be a while until my next sabbatical, but I'm thinking along the lines of a "Public Land Scramble" from the Pacific to the Plains without stepping off public lands.
Very good discussion, analysis, and interpretation. I've looked at the Town Pass fault just east of Town Pass and it has near-vertical fault striations on numerous exposures. Somewhere I have photos. I've always considered it to be a normal fault.
Hi Thom, thanks for the comment. My understanding is also that it is a normal fault. The next time I'm out that direction, I'll have pay more attention to that area. A stop at Towne Pass was never on my itinerary!
Since Death Valley is inside a National Park, it might be very difficult to collect intrusive geophysical data such as seismic reflection and refraction profiles. That would be the best way to see what is going on in the geology beneath the basin sedimentary section.
The current USGS geologic mapping of the park which has been delayed for 20 years due to funding and staffing issues since the early 2000's that is used by NPS internally for management purposes and is currently under renewed preparation for publication by the Geologic Framework of the Intermountain West Project (https://www.usgs.gov/centers/geosciences-and-environmental-change-science-center/science/geologic-framework#overview) strongly suggests exactly the fault you are proposing. There are surface exposures of uncertain Quaternary age offset and lineaments along this trend. Offsets have been identified in alluvium and paleo-spring deposits off the flank of the Cottonwoods south of Dry Bone Canyon and along several mapped strands of faulting on trend outboard of the ne edge of Tucki Mtn. Multiple lineaments are also identified along the western side of Cottonball Basin. This 100k map product has remained unpublished for 2 decades but we hope to have it re-reviewed and published in updated digital format in the next few years. Older regional mapping and sparse gravity data in the park was used to draw some earlier geophysically inferred structures moderately similar to your suggestion (https://pubs.usgs.gov/mf/2002/mf-2381/) but the seismic data absolutely supports the general trend you have drawn as a fault zone with probable late Miocene through younger motion. Faulting on the west side of Mesquite Flat was incorporated into the USGS regional cross sections (https://pubs.usgs.gov/mf/2001/mf-2370/), hydrostructural map (https://pubs.usgs.gov/mf/2002/mf-2372/), and regional groundwater flow model (https://pubs.usgs.gov/pp/1711/) but they were shifted too far west, and I agree with your location based upon my more recent and detailed mapping of the area.
I agree that the earthquake swarm/sequence is probably not on the Towne Pass fault. However, with respect to the text that states "Second, it is not known to be active based on surface geology", readers should be aware of the different uses of the term "active". For California, under the Alquist Priolo Earthquake Fault Zoning Act, "active" faults have moved in the past 11,700 years (Holocene-active) and if zoned by the state, have regulatory requirements for developments within these fault zones. The USGS, classifies the Towne Pass fault as "Late Quaternary active" (as evidenced by some impressive grabens and scarps at the range front), so has the potential to cause large earthquakes and is included as a seismic source in the USGS National Seismic Hazard Model. Regardless of the details, I like the possibility of Option 3 of an unmapped buried strike slip fault, which is consistent with what we have seen so far in this sequence.
Hi Tim, thanks for the comments on the classification of the Towne Pass Fault. I have updated the text with a mention of your comment, so anyone interested can follow up. Cheers - Kyle.
Sounds good to me. I'm always a proponent of unmapped faults. There's no recent scarp, but there is a suspicious NW-aligned row of hills, defining a straight line along their west sides, near the edge of the alluvial fan near there (e.g., 36.6, -117.0816).
As for the Towne Pass Fault, I agree that it's probably not the droid you're looking for, but it sure looks active to me. Maybe just a long recurrence interval? Here's a view from the ground, from my Mojave YouTube series:
https://youtu.be/sZpI8FUHv9s?si=biAEUOZM53MHGJFh&t=2708
Hi Nick, I remember that sequence from your intrepid crossing of Death Valley, because it was one of the few places where your track crossed my personal historical track. I do think a lot of these sub-mm-per-year kinds of faults can have big earthquakes, which means recurrence intervals of many thousands of years for the large events that break the surface.
I did see the row of hills you mention but couldn't convince myself that they were related to young faulting, so I left them out.
Do you have any plans for another epic trek? - Kyle
I agree those hills have no apparent Quaternary fault activity . . . but it's usually easier to reactivate an old fault than to tear a new one, eh? It'll be a while until my next sabbatical, but I'm thinking along the lines of a "Public Land Scramble" from the Pacific to the Plains without stepping off public lands.
Very good discussion, analysis, and interpretation. I've looked at the Town Pass fault just east of Town Pass and it has near-vertical fault striations on numerous exposures. Somewhere I have photos. I've always considered it to be a normal fault.
Hi Thom, thanks for the comment. My understanding is also that it is a normal fault. The next time I'm out that direction, I'll have pay more attention to that area. A stop at Towne Pass was never on my itinerary!