According to Metro Davao Site Response Atlas issued in 2019 by the Department of Science and Technology and the Philippine Institute of Volcanology and Seismology, Davao City has six active faults, namely: Lacson fault in Calinan District: Tamugan fault, New Carmen fault, and Colosas fault in Paquibato district; and Dacudao fault and Biao Eskwela fault in Tugbok district.
The Mati fault, however, is the most significant. Measured to be about 30 km long, the fault is linked to the 1,200-km Philippine Fault line, the longest in the islands. A good 320 kilometeers of this fault line is found in eastern Mindanao, from Surigao region to Mati City.
Nationwide, there are five active fault lines in the country so far discovered, i.e., the Western Philippine Fault, the Eastern Philippine Fault, the South of Mindanao Fault, the Central Philippine Fault and the Marikina/Valley Fault System.
Davao region’s vulnerability to tremors is found in Jesuit priest Fr. Miguel Saderra Maso’s Catalogue of Violent and Destructive Earthquakes in the Philippines 1599-1909 (1910), which was issued by the Weather Bureau, with executive control over Manila Central Observatory.
The inclusion of Davao in the list started in 1870, a good twelve years after it was conquered.
Fr. Maso, in his introduction, divided the earthquakes into classes following the Rossi-Forel Scale. Class I are tremors with “sufficient force to produce cracks in buildings and to throw down chimneys,” the equal of intensity VII. Class II, meanwhile, refers to earthquakes that destroy “walls and some weak structures,” the same with intensity VIII. The last classification are tremors causing “general destruction,” the equivalent of intensity IX and intensity X.
The first recorded tremor in Davao was on November 4, 1870 was intensity VII in the De Rossi-Forel scale, with epicenter “between the Gulf of Davao and the Province of Misamis.” This was followed by another violent intensity VI quake on June 28, 1871, that shook “throughout the region surrounding Davao Gulf, with frequent aftershocks during the ensuing 8 days.” That same year, on October 4, a more vicious intensity VII earthquake shook the region.
Capping the year’s list were three more forceful tremors. On November 5, a “very violent
and prolonged [intensity VII] earthquake” was “felt intensely throughout eastern Mindanao.” On December 8, a devastating intensity IX quake hit Cotabato and Davao, which is 120 kilomers away, and thereafter a “series of most violent shocks were experienced, accompanied by subterraneous rumblings.” And, on December 19, a “very violent [intensity VII] earthquake [shook] the length of Mindanao, from Surigao to Davao.”
Meanwhile, on August 24, 1872, the district of Davao was hit by a very strong and protracted intensity VI earthquake in the vicinity of Mount Apo. Between 1878 and 1894, there were very few strong quakes that shook southeastern Mindanao. Some of the most devastating tremors affecting the region had their epicenter in Agusan River Valley at the boundary of Davao.
On September 17, 1878, a destructive intensity VII quake hit Davao Occidental, which is west of the gulf of Davao. As a result, many of the buildings in town were destroyed, and the rumblings went on for another five days. A year later, on September 28, the district of Davao was shaken by a “very strong earthquake” recorded at intensity VI. A less intense quake also hit the area 14 days earlier.
The February 22, 1885, tremor was one of the most destructive on record at intensity VIII; it hit the east coast of Mindanao, mainly Davao Oriental and the regions facing the Pacific. Many of the standing concrete structures collapsed to the ground. Fr. Maso wrote:
“Destructive earthquake, which did extensive damage to the churches and other buildings of stone or wood and caused mighty fissures and landslides in the mountains as well as in the scarps of the Pacific coast.”
On February 10, 1894, southeastern Mindanao was again hit with an intensity VIII tremor.
This time the epicenter was in the region east of Davao Gulf, or Davao Oriental, and it inflicted damages in many towns and “produced many fissures and displacements in the mountains and cracked a few houses of wood in the towns of Mati and Sigaboy [now Gov. Generoso].” In 1903, two more earthquakes were recorded. The first was on May 24, with intensity VI, and the other was on December 28, with intensity VIII. The first was described as “[v]ery intense earthquake, having its center in the northwest of Davao Gulf” and the shock it created “was perceptible throughout the island [of Mindanao].”
The other tremble was a “destructive earthquake in the region east of Davao Gulf which damaged many houses in Mati, Caraga, Sigaboy, etc.” As a result, “[l]arge fissures opened and several displacements occurred in the limestone layers of the Pacific coast near Caraga.”