SCEC Award Number 16041 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Timing a late Holocene earthquake cluster on the Ash Hill fault, Eastern California Shear Zone
Investigator(s)
Name Organization
Christine Regalla Boston University
Other Participants Amani Alabri, Boston University PhD candidate;
Hannah Pangrcic, Boston University undergraduate student
SCEC Priorities 1a, 4c, 2b SCEC Groups SoSAFE, SDOT, Geology
Report Due Date 10/14/2016 Date Report Submitted 11/14/2016
Project Abstract
 Although the field and geochronologic research on the Ash Hill fault was not funded, I did receive funding to present on the current results of this project at the fall SCEC meeting. This was a great opportunity for me, an early career researcher from the east coast, to be able to join in the SCEC meeting for the first time. At this meeting I was able to interact with a range of geologists and geophysicists, and learn about ongoing research and initiatives within SCEC. In particular, I was able to discuss potential geochronologic techniques applicable to this project, including the potential pitfalls of OSL in southern California and the potential successes of IRSL. Additionally, I learned of the “Earthquake Gates” initiative of SCEC 5. Our preliminary work on the Ash Hill and Panamint faults in Panamint Valley suggests that the two faults may be seimogenically linked and may rupture in the same or related events. Strain transfer between these two faults systems is accommodated across a network of complex, young, surface ruptures. This site may be a key location for a case study on the role of a geometric “gate” that facilitates strain transfer between potentially geometrically linked faults in the northern ECSZ.
Intellectual Merit Paleoseismic investigations in the southern ECSZ reveal an ongoing cluster of seismicity since <1.5 ka, and suggest that earthquakes in the southern ECSZ alternate in time with those along the San Andreas fault. Recent investigations in the northern ECSZ show that late Holocene earthquakes on the Panamint, Garlock, and Owens Valley faults may cluster in time, in consort with clusters in the southern ECSZ, suggesting potential “mega-clusters” of earthquakes that occur across both the southern and northern ECSZ. Although the spatial and temporal patterns in seismicity are complex, these data point toward the potential for stress transfer between northern ECSZ faults and indicate that the Garlock fault may load the Mojave segment of the San Andreas fault. Understanding the spatial temporal evolution of clustered seismicity in the ECSZ, therefore, has implications for probabilistic seismic hazard in southern California. Recent mapping of alluvial deposits offset by the Ash Hill fault provide preliminary evidence for three ~M 6 -7 ruptures since the middle Holocene. These events may occur at similar times to those on the Panamint, Owens Valley, and Garlock faults, suggesting that the Ash Hill fault may be part of a system of faults in the northern ECSZ that have experienced a late Holocene cluster in seismicity. Our ongoing work on the Ash Hill fault therefore falls in accord with SCEC4 science objectives on: 1) Mapping and studying faults in Southern CA, to determine slip rates for faults at multiple time scales (objective 1a). 2) Investigating stress-mediated fault interactions and the documentation of clustered seismicity in the paleoseismic catalogue (objective 2b) and 3) Improved mapping of fault ruptures using LiDAR (objective 4c).
Broader Impacts The funding received from SCEC provided support for an early career female scientist to attend the SCEC meeting, learn of ongoing research and objectives within SCEC, and network within the earthquake geology community. In addition, the project on the Ash Hill fault, although not funded by SCEC, has supported an undergraduate research experience for one female undergraduate student, Hannah Pangrcic, as well as opportunities for field training for Hannah and three additional female students, Emily Rogalski (undergraduate), Emily Schottenfels (graduate), and Emerson Lynch (graduate). These students have received field training in the mapping of alluvial deposits, surface ruptures, off fault deformation, soil chronosequences, and OSL and Be10 sample collection. Hannah Pangrcic has additionally had the opportunity to present the results of her work on the Ash Hill fault at the 2016 Friends of the Pleistocene field trip and at the 2016 Boston University Undergraduate Symposium.
Exemplary Figure Figure 6: Detail surficial mapping, at a scale of 1:4,000, for a portion of the southern Ash Hill fault.