Towards Implementation of Multi-Segment Ruptures in the Broadband Platform: Composite Source Model

John G. Anderson

Published August 15, 2016, SCEC Contribution #6947, 2016 SCEC Annual Meeting Poster #265

One major goal of the Broadband Platform for 2016 is to implement multi-segment ruptures. One straightforward approach under consideration is to generate ground motions from each segment separately, and then add them with an appropriate time lag. Research on this is still underway, but some preliminary results can be reported on two issues: scaling of the two rupture segments, and sensitivity to the approach described above.

The scaling issue is illustrated by considering two segments of the San Jacinto fault considered by Lozos et al. (2015): the Claremont strand (L1=79 km) and the Casa Loma – Clark strand (L2=110 km). With the 21 km overlap of the strands, the end-to-end length is L3=168 km. For modeling, we need the sum of the moments of the two strands to equal the moment of the entire fault (Mo(L1)+Mo(L2)=Mo(L3)). Defining r=(Mo(L1)+Mo(L2))/Mo(L3), and using Wells and Coppersmith (1994) or Hanks and Bakun (2008), r= 0.77 and 0.65, respectively. Recently, we (Anderson, Biasi and Wesnousky, 2016) have proposed a scaling model that aims to have a constant stress drop over the entire range rupture lengths. This model gives r=1.03 for the above case, which is closer to unity than the other considered models, and thus an improvement. However, the ABW16 model is not so helpful when there are short fault segments, so additional thought is still required.

Examples of the effects of summing ground motions from the different segments, will be shown for the San Jacinto fault, emphasizing the cases of precariously balanced rocks discussed in the poster by Brune et al. nearby at this meeting.

Key Words
synthetic, strong-motion, time-histories, accelerograms

Citation
Anderson, J. G. (2016, 08). Towards Implementation of Multi-Segment Ruptures in the Broadband Platform: Composite Source Model. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motion Prediction (GMP)