Neotectonics and Paleoseismology of the Limon and Pedro Miguel Faults in Panama: Earthquake Hazard to the Panama Canal

Abstract

We present new geologic, tectonic geomorphic, and geochronologic data on the slip rate, timing, and size of past surface ruptures for the right-lateral Limón and Pedro Miguel faults in central Panamá. These faults are part of a system of conjugate faults that accommodate the internal deformation of Panamá resulting from the ongoing collision of Central and South America. There have been at least three surface ruptures on the Limón fault in the past 950-1400 years, with the most recent during the past 365 years. Displacement in this young event is at least 1.2 m (based on trenching) and may be 1.6-2 m (based on small channel offsets). A well-preserved 4.2 m offset suggests that the penultimate event also sustained significant displacement. The Holocene slip rate has averaged about 6 mm=yr, based on a 30-m offset terrace riser incised into a 5-ka abandoned channel. The Pedro Miguel fault has sustained three surface ruptures in the past 1600 years, the most recent being the 2 May 1621 earthquake that partially destroyed Panamá Viejo. At least 2.1 m of slip occurred in this event near the Canal, with geomorphic offsets suggesting 2.5-3 m. The historic Camino de Cruces is offset 2.8 m, indicating multimeter displacement over at least 20 km of fault length. Channel offsets of 100-400 m, together with a climate-induced incision model, suggest a Late Quaternary slip rate of about 5 mm=yr, which is consistent with the paleoseismic results. Comparison of the timing of surface ruptures between the Limón and Pedro Miguel faults suggests that large earthquakes may rupture both faults with 2-3 m of displacement for over 40 km, such as are likely in earthquakes in the M 7 range. Altogether, our observations indicate that the Limón and Pedro Miguel faults represent a significant seismic hazard to central Panamá and, specifically, to the Canal and Panamá City.

Kinematic reconstruction of the Caribbean region since the Early Jurassic

“…Prior to collision with the South American continent, the Panama-Chocó block formed a straight volcanic arc, that started to segment into the western, central, eastern and Greater Panama blocks during Late Eocene-Early Oligocene times (~28-38 Ma, Farris et al, 2011;Montes et al, 2012). Segmentation and deformation was achieved by vertical axis rotation of the individual blocks and local folding and faulting (Rockwell et al, 2010;Montes et al, 2012). In our reconstruction, we follow the model of Montes et al (2012) for the Panama-Chocó block.…”

Anthropic Rock: a brief history

“…Man's most ancient stone monuments, the wonders of Greece and Egypt for example, might be shielded by such installations from destructive earth temblors (Tassios, 2010). And, on a much larger geographical scale, for instance, the Panama Canal, currently undergoing a costly expansion to permit more and larger ship traffic, is vulnerable to major earthquakes on two nearby faults (Rockwell et al, 2010). Such artificial dikes may even become identified as in many ways similar to keiroliths (fault rocks and mélanges) found, for instance, at Earth-crust subduction sites and fault offset zones (Sengor and Sakmc, 2001).…”

Three-Dimensional Investigation of a 5 m Deflected Swale along the San Andreas Fault in the Carrizo Plain

“…The initial focus of our investigation was to confirm the ∼4:7 m slip and/or correct for any pre-earthquake deflections by following the upstream end of the buried channel thalweg into the fault zone and out through the downstream end. This method has been successfully applied to investigation of channels at numerous locations (e.g., Wesnousky et al, 1991;Grant and Sieh, 1993;Liu et al, 2004;Liu-Zeng et al, 2006;Rockwell et al, 2010).…”

“…(2) How much deflection, if any, has contributed (either adding or subtracting from the true offset) to the measured offset amount along fault strike? Many deflected channels are easy to identify and eliminate from consideration for slip measurements, but a subtly deflected channel is difficult to identify unless the swale is excavated and traced toward and away from the fault zone of interest (e.g., Wesnousky et al, 1991;Liu et al, 2004;Liu-Zeng et al, 2006;Rockwell et al, 2010). In this study, we address these questions through geomorphic analysis with LiDAR data and 3D excavation of a deflected swale that was not included in any previously published dataset.…”