Determining Histories of Slip on Normal Faults With Bedrock Scarps Using Cosmogenic Nuclide Exposure Data. Issue 3 (10th March 2021)

• Record Type: Journal Article
• Authors: Goodall, H. J.; Gregory, L. C.; Wedmore, L. N. J.; McCaffrey, K. J. W.; Amey, R. M. J.; Roberts, G. P.; Shanks, R. P.; Phillips, R. J.; Hooper, A.
• Is Part Of: Tectonics. Volume 40:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-10
• Subjects: active tectonics -- cosmogenic isotopes -- fault slip rates -- quaternary dating -- quaternary geomorphology; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2020TC006457
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: Cosmogenic exposure data can be used to calculate time‐varying fault slip rates on normal faults with exposed bedrock scarps. The method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to determine the slip rate of a fault. Here we show that by applying strict sampling criteria and using geologically informed modeling parameters in a Bayesian‐inference Markov chain Monte Carlo method, similar patterns of slip rate changes can be modeled at multiple sites on the same fault. Consequently, cosmogenic data can be used to resolve along‐strike fault activity. We present cosmogenic 36 Cl concentrations from seven sites on two faults in the Italian Apennines. The average slip rate varies between sites on the Campo Felice Fault (0.84 ± 0.23 to 1.61 ± 0.27 mm yr −1 ), and all sites experienced a period of higher than average slip rate between 0.5 and 2 ka and a period of lower than average slip rate before 3 ka. On the Roccapreturo fault, slip rate in the center of the fault is 0.55 ± 0.11 and 0.35 ± 0.05 mm yr −1 at the fault tip near a relay zone. The estimated time since the last earthquake is the same at each site along the same fault (631 ± 620 years at Campo Felice and 2, 603 ± 1, 355 years at Roccapreturo). These results highlight the potential for cosmogenic exposure data to reveal the detailed millennial history of earthquake slip on active normal faults. Key Points: Fault slip rates constrained with cosmogenic isotopes from multiple sites on the same fault agree Fault slip rate varies during the Holocene, and pulses of rapid slip rate are temporally correlated along strike Cosmogenic isotopes on bedrock fault scarps provide a detailed record of activity, provided the sample locations are carefully selected