Chiou and Youngs PEER-NGA Empirical Ground Motion Model for ...

Rupture Distances and Source-Site Geometry: One hundred and ten of the 173
earthquakes in the PEER-NGA database do not have associated finite fault models that can
be used to compute the standard closest distance to rupture measures (e.g. rupture distance
RRUP and Joyner-Boore distance, RJB) and the source-site geometry parameters such as
hanging wall and foot wall positions and the source-site angle θSITE. Use of hypocentral
distance, RHYP, and epicentral distance, REPI, for RRUP and RJB, respectively, introduces a bias
in the values as in most situations RRUP < RHYP and RJB > REPI, event for small events. The
various geometry and distance measures for these earthquakes were estimated by simulating
earthquake ruptures using the earthquake size and known or inferred information on the
hypocentral depth, fault strike, fault dip, and rupture mechanism. Appendix B describes the
simulation process. Figure 3 shows the ratios of RJB/REPI and RRUP/RHYP for the 702
recordings from the 110 earthquakes and indicates the magnitude of the bias that could be
introduced by using REPI for RJB and RHYP for RRUP. The analysis also provided estimates of
the depth to the top of rupture, ZTOR, and rupture width, W, for these earthquakes.
R_JB / R_EPI
R_RUP / R_HYP
1.0
0.8
0.6
0.4
0.2
0.0
1 10 100 1000
1.0
0.8
0.6
0.4
0.2
R_EPI (km)
0.0
1 10 100 1000
R_HYP (km)
Figure 3: Ratio of estimated values of RJB and RRUP to REPI and RHYP for recordings from earthquakes
without finite fault models in the PEER-NGA database.
C&Y2006 Page 9