Page 4 - Demo

1850 | Geof%u00edsica Internacional (2026) 65-1Since all peak values at OXLC are high during 08/09/2017, greater damage during this event at MAPN is to be expected, followed by the 2020 event. PGA during 1999 is about twice the value during 2012, while PGV and PGD are greater during the latter event. Greater damage in 1999 than in 2012 would suggest that the intensity is better correlated with PGA than PGV and PGD. The high peak values during 2020 point to an event with greater damage potential than other events except for the earthquake of 2017. Lesser damage during 2020 event as compared to 1999, if true, may have been a consequence of the recovery and conservation efforts following the earthquakes of 30/09/1999 and 08/09/2017 which had adequately strengthened the vulnerable structures.3. Accelerographic Network of Monte Alb%u00e1nDamage during the 30/09/1999 earthquake led to the installation of a 12-channel accelerographic network on the North Platform of the Monte Alb%u00e1n (MAPN). It consisted of three external and one internal triaxial sensor (Table 2). The recordings were made at 100 samples/s. The sensors were installed at the base and the top of the structure. At mid-height both internal and external triaxial sensors were deployed (Figure 3). First available recording by the network dates back to 13/03/2004. The network stopped working in August 2011 due to maintenance problem. The instrumentation was rehabilitated in June 2019 but only with the triaxial internal sensor located at mid-height. This accelerograph recorded earthquakes until May 2023 after which it ceased to work. The instruments were withdrawn in August 2024. Presently, there is no seismic sensor in operation at the archaeological site.4. Estimation of Ground Motion at Monte Alb%u00e1n during Recent Large EarthquakesGround motions at Monte Alb%u00e1n may differ from those at OXLC because of topographic and local site effects (altitude above MSL: OXLC 1542 m, Monte Alb%u00e1n 1942 m; Figure 1, Table 2). Since ground motions at OXLC are known, we estimate the motions at Monte Alb%u00e1n using transfer functions between OXLC and Monte Alb%u00e1n and applying random vibration theory (see, Boore, 2003, for details). This methodology has been successfully used in Mexico (see, e.g., Ordaz et al., 2017) and elsewhere (Boore, 2003).We estimate spectral ratios (also denoted here as transfer functions) between Monte Alb%u00e1n and OXLC using accelerograms of events recorded simultaneously at both sites.Table 1a. Six large earthquakes whose recordings at OXLC are used to estimate ground motions at North Platform, Monte Alb%u00e1n (MAPN) via spectral ratio and random vibration theory. Note that the earthquake of 23/06/2020 was also recorded at mid-height of MAPN.Event Date Lat (%u00b0N) Long (%u00b0W) H, km MwFocal Mechanism R to OXLCkm%u0394 toOXLC %u03a6%u00b0 %u0151%u00b0 %u03bb%u00b0 km1 15/06/1999 18.15 97.52 60 6.9 309 40 -82 159 1472 30/09/1999 16.00 97.02 54 7.5 300 49 -78 130 1183 20/03/2012 16.25 98.53 20 7.5 296 10 95 216 2154 08/09/2017 14.76 94.10 46 8.2 318 78 -93 383 3805 19/09/2017 18.41 98.71 57 7.1 300 44 -83 263 2576 23/06/2020 15.80 96.13 17 7.4 268 16 61 154 153Table 1b. PGA, PGV, and PGD at OXLC during the six large earthquakes.Event Date PGA at OXLC, cm/s2 PGV at OXLC, cm/s PGD at OXLC, cmNS EW Z NS EW Z NS EW Z1 15/06/1999 23.5 18.3 13.0 1.90 1.72 1.00 0.32 0.58 0.252 30/09/1999 70.1 74.7 48.3 5.02 4.90 4.04 2.64 2.09 2.263 20/03/2012 37.2 27.7 32.9 6.57 4.66 5.16 4.33 3.61 5.144 08/09/2017 58.6 102.3 67.5 7.64 9.06 6.20 14.1 9.34 7.265 19/09/2017 22.5 21.8 12.1 1.38 2.02 1.28 0.37 0.59 0.256 23/06/2020 72.5 82.9 30.4 8.54 10.0 6.10 3.47 4.61 4.34