Large Holocene ruptures on the Canada David low angle normal fault, Baja California, Mexico

Keene W. Karlsson, Thomas K. Rockwell, John M. Fletcher, Paula M. Figueiredo, Jaziel Froylan Cambron, Allen M. Gontz, Sambit Naik, Pierre Lacan, Ronald M. Spelz, & Lewis A. Owen

Submitted July 31, 2020, SCEC Contribution #10217

We present the results of detailed mapping and paleoseismic investigations along the southwestern flank of the Sierra El Mayor, a NW-SE trending mountain range in Baja California, Mexico, within a transtensive oblique rift boundary between the East Pacific Rise to the south and the San Andreas fault system to the north. We mapped a 2 km-long section of the complex fault scarp array associated with the Cañada David detachment, a low-angle oblique normal fault, using high-resolution unmanned aerial vehicle imagery. A sequence of alluvial fans that comprise a bajada that flanks the southwestern range front along this section were also mapped, and their ages distinguished based on a regional soil chronosequence. Soil pits were excavated within seven alluvial fan surfaces of different ages and the soil characteristics were described for each. Three paleoseismic trenches were excavated across active surface faults that root into the Cañada David detachment at depth. Stratigraphic units in the trenches were described in detail, and samples were collected for optically stimulated luminescence (OSL) dating. The three trenches in this study show strong evidence for four large (Mw ≥7) Holocene earthquakes at or just prior to about 1.5-1.9, 3.9-4.7, 6.9-8.1 and 7.75-8.9 ka, as well as weak to moderate evidence for two additional late Pleistocene earthquakes at or just prior to 11.4-14.1 ka and 14.0-16.8 ka, indicating an average recurrence of such events at 2.5-3 ka. This earthquake recurrence interval is slightly longer than that for the Laguna Salada fault to the north that flanks the Sierra Cucapah. The regular recurrence of major surface ruptures strongly suggests that severely-misoriented low-angle normal faults like the Cañada David detachment have a mechanical behavior that is very similar to other more optimally oriented faults suggesting that earthquakes on such faults should be common and may be difficult to recognize from seismologic methods alone.

Citation
Karlsson, K. W., Rockwell, T. K., Fletcher, J. M., Figueiredo, P. M., Froylan Cambron, J., Gontz, A. M., Naik, S., Lacan, P., Spelz, R. M., & Owen, L. A. (2020). Large Holocene ruptures on the Canada David low angle normal fault, Baja California, Mexico. Tectonics, (submitted).


Related Projects & Working Groups
Paleoseismology and mechanics of multi-fault ruptures, Earthquake Geology