THE AD 1621 PANAMA VIEJO EARTHQUAKE, THE CAMINO DE CRUCES, AND THE PEDRO MIGUEL FAULT IN PANAMA: AN ARCHEOSEISMOLOGY SUCCESS STORY

Using a historical Spanish Road, the “Camino de Cruces” (CdC), as a piercing line across the Pedro Miguel fault (PMF), we undertook a detailed study to determine if rupture of the PMF generated the AD 1621 “Panama Viejo” earthquake. The CdC was constructed about 1526-1536 using rounded basaltic cobblestones that are not native to the local area. By mapping the tectonic geomorphology and hand excavating trenches and stream banks, we exposed the PMF through the area where it crosses the CdC. Fault exposures demonstrate that the youngest alluvial deposits are offset, and the fault continues to the surface, overlain only by the uppermost 6 cm of organic topsoil. The CdC is sharply deformed where it crosses the northern end of the PMF. Trail cobbles are incorporated into, and overthrust by, the most recent fault scarp, and the CdC shows evidence for having been rebuilt across the fault. Using the trail offset and measurements of the small geomorphic offsets in the immediate area, reconstruction of the pre-earthquake landscape yielded a well-defined fault displacement of 2.8-3.0 meters. Because the rupture must have occurred post-1536 AD, and no other historical seismic event was as strongly felt in Panama until 1882, we conclude that the PMF generated the earthquake that destroyed Panamá Viejo on May 2, 1621, creating severe damage to the city’s stone buildings. As such, the PMF becomes the controlling structure for the seismic hazard to the Panama Canal and modern Panama City.