Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Table 1: Principal slip on fault ZFMA2 and PFC- predicted induced slip on known nearby faults. Modified from Yoon and Zang, 2019, their Table 8-4. m from a hypothetical M5.5 event on ZFMA3, with D=0.32 m. Their “d” values ranged from 20 to 80 mm (Table 1). Our values from empirical equations ranged from 9 to 14 mm (Nurminen) and 117 to 158 mm (Moss), thus bracketing the Yoon values. Table 1. Principal slip on fault ZFMA2 and PFC- predicted induced slip on known nearby faults. Modified from Yoon and Zang, 2019, their Table 8-4. ACTIV- ATION DEFORM. ZONE SLIP (m) Mag. Mw Distance from ZFMA2 (m) “d” from Nurminen equation (m) “d” from Moss equation Primary ZFMA2 0.32 5.5 n/a Secon- dary ZFMA1 0.08 4.32 850 0.0111 0.1488 ZFMA3 0.08 4.27 1150 0.0091 0.1376 ZFMWNW0003 Eckfjärdin Fault 0.02 4.03 600 0.0139 0.1588 ZFMWNW0001 Singö Fault 0.03 4.15 1770 0.0069 0.1171 ZFMWNW0004 Forsmark Fault 0.02 4.02 1100 0.0094 0.1394 Yoon and Zang also simulated an M6.05 earthquake on the regional, vertical Singö fault (D=0.72 m) and calculated induced displacements on the Eckfjärdin, Forsmark, and three ZFMA faults ranging from 20 to 120 mm. We calculated the distributed displacements from the Petersen et al. (2011) equations for strike-slip faults. Petersen equation 20 predicts “d” based on magnitude and distance, with values ranging from 15 to 24 mm, just overlapping the lower part of the Yoon range. Petersen equation 21 predicts “d/Dmax” as a function of distance, with values ranging from 40 to 64 mm, which lies in the center of Yoon’s range. The closest correspondence of any empirically- predicted “d” values with numerically-predicted “d” values appears to be in this last case above, where “d” was being predicted on pre-existing deformation zones (DZs). Where “d” was predicted on smooth fractures, the empirical predictions were always larger Yoon and Zang also simulated an M6.05 earthquake on the regional, vertical Singö fault (D=0.72 m) and calculated induced displacements on the Eckfjärdin, Forsmark, and three ZFMA faults ranging from 20 to 120 mm. We calculated he distributed displacements from the Petersen et al. (2011) equations for strike- slip faults. Petersen equation 20 predicts “d” based on magnitude and distance, with values ranging from 15 to 24 mm, just overlapping the lower pa t of the Yoon range. Petersen equation 21 predicts “d/Dmax” as a function of distance, with values ranging from 40 to 64 mm, which lies in the center of Yoon’s range. The closest correspondence of any empirically- predicted “d” values with numerically-predicted “d” values appears to be in this last case above, where “d” was being predicted on pre- existing deformation zones (DZs). Where “d” was predicted on smooth fractures, the empirical predictions were always larger to much larger than the numerical “d” values. This suggests that the distributed faults mapped in post- earthquake reconnaissance in the field may have mostly been the result of reactivating pre- existing shear zones, rather than smooth fractures. If that is the case, it is improper to use the present empirical equations to predict shear on smooth target fractures, but only shear on other DZs. In other words, the smaller 3DEC-predicted displacements are probably appropriate for design use on clean fractures, but should not be used for longer, thicker shear zones. For those the PFC code should be used, and then modified by comparing it to the empirical predictions.