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S.K. Singh et al. | 1859January 1931 (Mw 7.8), an event that was greatly destructive to the city of Oaxaca (Singh et al., 1985).Exceedance curve from standard probabilistic seismic hazard analysis (PSHA) at a site such as OXLC is also shown in Figure 8. The tectonic setting and seismicity data for the PSHA model is described in detail in Ordaz et al. (2024). For PSHA computations we considered the GMPEs of Arroyo et al. (2010) for interface events, Garc%u00eda et al (2005) for intraslab events, and Abrahamson and Silva (1997) for crustal events.The three (PGA)H exceedance curves for OXLC based on (1) 25-years of observed values, (2) 124 years of partly observed and partly estimated values, and (3) standard PSHA, are in reasonable agreement with each other. As mentioned earlier, (1) is based on only 25-year data. Even though a catalog of 124 years of significant events is considered for (2), the errors in location of older events and the estimated values from GMPEs affect the exceedance curve. The PSHA curve suffers some of the same shortcomings as (2); additionally, it is based on assumptions, such as the validity of seismicity models and the ergodic assumption of GMPEs, which may not hold good. In these circumstances, we give greater credence to (2) for the hazard levels of interest.As mentioned earlier, damage at Monte Alb%u00e1n seems to occur when (PGA)H at OXLC exceeds 70 cm/s2 (or, equivalently, ~120cm/s2 at the base of Monte Alb%u00e1n if we take an amplification factor of 1.72 corresponding to intraslab events, Table 6). From Figure 8, this level of (PGA)H exceeds about every 20 yrs.Similarly, (PGA)H at OXLC exceeds 100 cm/s2 and 250 cm/s2(equivalently 172 cm/s2 and 430 cm/s2 at the base of Monte Alb%u00e1n) every 62 and 116 yrs, respectively. An extrapolation in Figure 8 suggests that (PGA)H of 560 cm/s2 at OXLC (963 cm/s2at the base of Monte Alb%u00e1n) is exceeded ~ 1000 yrs. This may have happened during the great, interface, Oaxaca earthquake of 1787 (Su%u00e1rez and Albini, 2009). Needless to emphasize that extrapolation of 124 yrs of data to infer return period of very high acceleration is a highly speculative exercise.6. ConclusionsOur estimated peak horizontal ground accelerations, (PGA)H, at Table 7. List of events during 1900-2024 which produced PGA* > 15 cm/s2 at OXLC (17.060N, 96.700W).Event No. Date Lat%u00b0NLong %u00b0WDepthkmM Rkm(PGA)H*, cm/s2at OXLC1 10/02/1928 18.26 97.99 84 6.5 209 (17)2 22/03/1928 16.02 96.30 20 7.5 125 (47)3 17/06/1928 15.93 96.76 20 7.6 127 (53)4 04/08/1928 16.07 98.02 20 7.4 179 (17)5 09/10/1928 16.53 97.34 20 7.6 92 (107)6 15/01/1931 16.34 96.87 40 7.8 91 (279)7 26/07/1937 18.48 96.0 85 7.3 194 (72)8 11/10/1945 18.32 97.65 95 6.5 196 (24)9 24/05/1959 17.72 97.72 80 6.8 153 (55)10 23/08/1965 16.08 95.87 20 7.5 141 (36)11 02/08/1968 16.52 97.74 20 7.3 127 (34) 12 28/08/1973 18.30 96.53 82 7.0 161 (69)13 29/11/1978 15.76 96.80 20 7.6 145 (39)14 24/10/1980 18.03 98.27 65 7.0 209 (25)15 15/06/1999 18.15 97.52 60 6.9 159 21.116 30/09/1999 16.00 97.02 54 7.5 130 72.417 23/03/2012 16.25 98.53 20 7.5 209 32.818 08/09/2017 14.76 94.10 46 8.2 383 83.419 19/09/2017 18.41 98.71 57 7.1 263 22.220 16/02/2018 16.22 98.01 20 7.2 169 (17) 22 23/06/2020 15.80 96.13 17 7.4 154 77.9*(PGA)H = [{(PGA)NS2 + (PGA)EW2}/2]1/2. Without parenthesis: recorded values, in parenthesis: estimated from GMPEs. Multiply (PGA)H at OXLC by 1.72 and 1.79 to get (PGA)H at the base of MAPN for intraslab and interface events, respectively.