Historical and Paleoseismic Evidence of the 1879 Mw 7.4 Surigao Earthquake, Philippines

The 1879 Mw 7.4 Surigao earthquake was considered as one of the largest and most damaging earthquakes in the southern part of the Philippines. It occurred along the Surigao segment of the Philippine fault, a major strike-slip fault that has relatively few surface rupturing earthquakes. Based on written historical records, this earthquake generated strong ground shaking that caused significant damages to infrastructures such as churches and buildings near the epicentral area. Widespread liquefaction and landslides were also described. A significant account of this earthquake is a detailed description of the surface rupture. Through aerial photograph
interpretation, geologic mapping, and paleoseismic investigation, we identified the 100-km-long surface rupture during the 1879 Surigao earthquake. The surface rupture
was manifested by continuous tectonic scarps and offset creeks. In two paleoseismic trenches, we also identified evidence of at least two and probably four surface-rupturing earthquakes including the 1879 event during the past 1300 years. If we assume that the coseismic lateral displacement of the 1879 Surigao earthquake is at
least 5 m, the slip rate along this segment is calculated to be 5-17 mm/yr, which is comparable with the GPS measured slip rate and with a recurrence interval of about
300-1000 years.