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1848 | Geof%u00edsica Internacional (2026) 65-11. IntroductionConstruction of the magnificent archaeological site of Monte Alb%u00e1n, overlooking the Valley Oaxaca, began in 500 BC. It became the center of economic, political, and religious power of the Zapotec civilization that flourished until 700AD when its slow decline began. At its peak it had a population of about 30,000. Monte Alb%u00e1n was the first urban complex in Meso America. Several causes of decline and dispersion of the population have been suggested: environmental factors, conflict with neighboring Mixtec civilization, fire, and social turmoil. It was not until 19-th century that local and European explorers began reporting of its existence. First detailed exploration of Monte Alb%u00e1n was carried by Leopoldo Batres (Batres, 1902) during the presidency of Porfirio D%u00edaz. Between 1930 and 1957 an extensive archaeological exploration was carried out under the leadership of Alfonso Caso. In 1987 Monte Alb%u00e1n was designated a UNESCO World Heritage Site. Archaeological and preservation work at Monte Alb%u00e1n still continues. The majestic site is an important tourist attraction.As large subduction thrust earthquakes along the Pacific coast and intraslab events in the subducted Coos plate below the State of Oaxaca are relatively frequent, the archeological site must have been subjected to severe ground motion many times. Thus, it was not a surprise that the normal-faulting, intraslab earthquake of 8 September, 2017 (Mw 8.2) caused significant damage to the archaeological site of Monte Alb%u00e1n (Figure 1). Collapse of walls, and fractures and fissures in walls and structural elements were reported. Eleven monuments at the Monte Alb%u00e1n archaeological site suffered damage. The damage was partly attributed to previous poor interventions and lack of adequate attention and absence of maintenance over many years. An excellent and extensive report on earthquake recovery, stabilization, and conservation at Monte Alb%u00e1n and the neighboring monumental zone of Atzompa is given in Robles Garc%u00eda et al.(2022). Previously, Monte Alb%u00e1n had suffered damage during the 30 September, 1999 (Mw7.5) earthquake (Robles Garc%u00eda et al., 2009) which was also an intraslab event (Figure 1).To understand the seismic hazard faced by the archaeological site and to adequately strengthen it against damage during future events, it is desirable to know the ground motions at Monte Alb%u00e1n during previous large earthquakes, especially those of 2017 and 1999, and exceedance rate of such motions. Unfortunately, there is no on-site recording of these earthquakes. No accelerograph was installed at Monte Alb%u00e1n in 1999. Although an accelerographic network was put in place in 2004, it was not in operation during 2011 - 2019.There are, however, several accelerographs in and near the city of Oaxaca. One station, OXLC, located on hard Cantera rock, is 7 km from Monte Alb%u00e1n (Figure 1). Beginning June 1999, most of the significant earthquakes are well recorded at OXLC. The recordings at this nearby station provide first, but quite likely, lower estimate of ground motion at Monte Alb%u00e1n. A lower estimate is likely due to expected amplification of seismic waves caused by the location of Monte Alb%u00e1n on a hill, about 400 m above the floor of the central Valley of Oaxaca where OXLC is located (Figure 1).If, however, we know the transfer function (i.e., spectral ratio) of ground motion at a site at Monte Alb%u00e1n with respect to OXLC, then the recordings at OXLC can be used to estimate the ground motion at this site of Monte Alb%u00e1n through the application of random vibration theory. We follow this methodology. OXLC is only 7 km from Monte Alb%u00e1n and mean H/V curve computed from 344 recordings at OXLC, reveals no significant site effect. Hence, it is an ideal reference station.2. Recordings of Significant Recent Earthquakes at Las Canteras (OXLC)The first recording at OXLC is from the 15/06/1999 (Mw6.9) Tehuac%u00e1n earthquake. Table 1a lists the six earthquakes which produced the largest ground motion at OXLC (and, hence, we expect, also at Monte Alb%u00e1n) in the period 1999 %u2013 2024. Four of the six events are normal-faulting intraslab and two are subduction, interface, thrust earthquakes. Figure 2 illustrates the accelerogram, velocity and displacement traces, as well as the Fourier acceleration spectra (FAS) of each of the six earthquakes. Peak ground acceleration (PGA), velocity (PGV), and displacement (PGD) values are compiled in Table 1b. As seen from Figure 2 and Table 1b, the PGA values during 30/09/1999, 08/09/2017, and 2020 earthquakes are very similar; PGV values are similar during 30/09/1999, 2012, 08/09/2017, and 2020; PGD is highest during 08/09/2017 while the values are similar during 2012 and 2020 earthquakes.Correlation of damage (intensity) with PGA, PGV or PGD is not straightforward (e.g., Wald et al., 1999; Wu et al., 2003; Sokolov and Furumura, 2008). Let us assume that the ground motions parameters at MAPN are proportional to those at OXLC. (We come back to this issue in a later section). If PGA is mainly responsible for damage at Monte Alb%u00e1n, then the earthquakes of 30/09/1999, 08/09/2017, and 2020 should have been equally damaging. This was not the case: the damage was more severe in 08/09/2017 than in 1999. Just what happened in 2020 is not clear from the report of Robles Garc%u00eda et al. (2022). If damage is related to PGV, then equal damage would have occurred in 2012, 08/09/2017, and 2020. Again, similar to 2020, there is no reports of damage in 2012. If PGD is the critical factor then the highest damage would have been expected in 2017 followed by 2012 and 2020 events.