SCEC Award Number 12128 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Validation of broadband ground-motion synthetics using earthquake engineering-relevant metrics
Investigator(s)
Name Organization
Kim Olsen San Diego State University
Other Participants 1 graduate researcher (3 summer mos, 2 mo acad year). No charge for PI
SCEC Priorities 6e, 6c, 6a SCEC Groups GMSV, GMP, EEII
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 We have simulated broadband (BB) ground motion synthetics for the M6.7 Northridge, CA, earthquake using the hybrid method by Mai et al. (2010). The bias of spectral accelerations between data and synthetics at 28 near-field stations is less than 0.5. We then generate map-based goodness-of-fit (GOF, Olsen and Mayhew, 2010) values for Northridge inelastic/elastic (IE) ratios for the bandwidths 0.2-0.5 s, 0.75-1.5 s, and 2-5s. The GOF scale ranges from 0 (poor) to 100 (best). The short-period IE ratios are poorly modeled, generally with GOF values < 40-50. The IE GOF values increase somewhat in the intermediate range, with most near-field station values in 45-65 range. Finally, the long-period IE ratios are generally in the range 55-75. When the IE ratios are plotted as a function of period and the ratio R (elastic displacement to yield displacement) the data and synthetics are very close for periods between 0.4 and 10 s, but start to diverge at shorter periods. Usually, but not for all stations, the synthetic IE ratios underpredict data for the intermediate to shorter periods. This matches the results from Olsen and Mayhew (2010) for the smaller M5.4 Chino Hills earthquake, and suggests the need for refining the BB method by Mai et al (2010) when used to compute IE ratios at shorter and intermediate periods. Future work should include additional scenarios, and compute the IE ratios using additional BB methods, such as the Graves and Pitarka (2010) and Liu et al. (2006) methods.
Intellectual Merit It is a SCEC priority to further the communication between Earth scientists and engineers. This work shows that the current state-of-the-art BB generation methods do not match the data in terms of inelastic/elastic displacement ratios for the higher frequencies. Thus the results warrants some attention to improving this aspect of the methods in the future for use by engineers.
Broader Impacts Improving the BB generation methods will translate into better seismic hazard analysis. Once the methods are adequate, they can be used by structural engineers for design.
Exemplary Figure Figure 3. Map-based GOF of Northridge IE ratios for (left) 0.2-0.5 s, (center) 0.75-1.5 s, and (right) 2-5s. Credits: Rumi Takedatsu.