Events : The October 15 Bohol Earthquake

At about 8:00 A.M. today (October 15, 2013),  a very strong earthquake struck the Central Visayas region. The earthquake's epicenter was located near Cabigtian town in Bohol Island. The earthquake also affected  parts of Mindanao and nearby islands, particularly Cebu. Bohol and Cebu took the brunt  of the earthquake, both islands suffered extensive infrastructure damage and quite a number of casualties. Determining the extent of damage and the number of casualties in both provinces is still in progress up to this moment. 

February 6 of last year, the same area was also struck by an earthquake of almost the same magnitude as the temblor today. Then, the island of Bohol was slighlty affected by the temblor and spared from any damage. This time the whole island of Bohol is much affected, and devastated at that. Bohol's booming tourist industry will surely suffer in the aftermath of the earthquake. Quite a number of its historical  century-old Catholic churches collapsed or were partially destroyed. Even the province's main tourist attraction : the famous"Chocolate Hills" were not spared from landslides. 

The strength of the Bohol earthquake was described by Phivolcs Director Renato Solidum as : “A magnitude seven earthquake has an energy equivalent to around 32 Hiroshima atomic bombs. This one had a magnitude of 7.2.”

Bohol Island has its own faultline : the East Bohol Fault (see picture below). Movements of faults and tectonic plates normally cause earthquakes.

USGS ShakeMap : Octber 15, 2013  Bohol Earthquake

Active Earthquake Faultlines of Bohol, Cebu and Negros Islands

Bohol Earthquake Epicenter

Types of Earthquake Faultline  Movement 

Normal faults are dip-slip faults within the upper plate (the upper portion of the inclined fault) subducting. Reverse faults are dip-slip faults with the upper plate rising. When people stand facing a fault, the right-lateral strike-slip faults are those in which the far surface has lateral slip to the right, while left-lateral strike-slip faults are those in which the far surface has lateral slip to the left. 

Source : http://www.hp1039.jishin.go.jp/eqchreng/af1-2.htm

According to the US Geological Survey, the Bohol earthquake was due to reverse faulting movement of a faultline. ( see illustration above ) :

"The October 15, 2013 M 7.1 earthquake near the city of Catigbian on Bohol Island, Philippines, occurred as the result of shallow reverse faulting on a moderately inclined fault dipping either to the northwest, or to the southeast. The depth of the event indicates it ruptured a fault within the crust of the Sunda plate, rather than on the deeper subduction zone plate boundary interface. At the latitude of this earthquake, the Philippine Sea plate moves towards the west-northwest with respect to the Sunda plate at a rate of approximately 10 cm/yr, subducting beneath the Philippine Islands several hundred kilometers to the east of the October 15 earthquake at the Philippine Trench."

"The Philippine Islands straddle a region of complex tectonics at the intersection of three major tectonic plates (the Philippine Sea, Sunda and Eurasia plates). As such, the islands are familiar with large and damaging earthquakes, and the region within 500 km of the October 15 earthquake has hosted 19 events of M6 or greater, a dozen of which have been shallow (0-70 km). One of these, a M 6.8 earthquake 70 km to the east of the October 15, 2013 event in 1990, caused several casualties."
Source : http://earthquake.usgs.gov/earthquakes/eventpage/usb000kdb4#summary

My prayer goes to all the people affected by the earthquake. And I fervently wish and pray that God heals our land soon.

Reminder :
Our fellow Filipinos affected by the earthquake in Bohol and Cebu surely need help now and in the days to come. Let's help them in anyway we can. Please don't forget to send your donations. God Bless everyone!


Picture and Map Sources :
http://www.hp1039.jishin.go.jp/eqchreng/af1-2.htm
http://www.phivolcs.dost.gov.ph/images/active.faults/af_trench_with_capitals.pdf
http://earthquake.usgs.gov/earthquakes/eventpage/usb000kdb4#summary

Related Link :
http://theprojectreview.blogspot.com/2012/02/information-february-6-negros-and-cebu.html

Information : PHIVOLCS - Valley Fault System Maps

I never thought I would actually encounter this kind of a listing. . . .

A few weeks ago, a fellow RESP and I got a real property listing from a house owner. It's a beautiful house and lot in a very nice location in Pasig City. I was suppose to offer the property to a client, but decided to first check the location of the property with the PHIVOLCS-Valley Fault System Maps just to make sure the property doesn't straddle on an earthquake fault line. Pasig City has its own share of this geological anomaly being part of the West Valley Fault Line. I'm glad I checked because I found out that the property is literally on the edge of an active fault line.

According to Phivolcs (Philippine Institute of Volcanology and Seismology), a house near a fault line is safe as long as the house has a buffer area of five or more meters from the actual fault line. 

Many real estate service practitioners are familiar with earthquake fault lines, but many are not familiar with the availability of the Valley Fault Maps which give the exact location of the fault lines in cities and towns which are part of the West Valley Fault Line. I'm sure the owner of the house who gave me the listing is also not familiar with the PHIVOLCS-Valley Fault System Maps. And I'm very sure that he didn't know the lot he built his house on lies on a fault line. He would never have built a house in that lot if he knew about it. Perhaps, he recently found out about it and wants to dispose the property.

Anyway, I decided not to offer the property anymore, and exclude it from my listings. 

There is an important lesson to learn from this experience, as real estate service practitioners, we need to give due diligence not only on the documents of the properties we deal, but also on the environmental and geological information concerning the properties. RESPs Beware!

Pasig City Fault Line  Map

Click map to enlarge

Valley Fault System Index Map

Click link below for Pasig City Valley Fault Line Map [PDF Format] :
http://www.phivolcs.dost.gov.ph/html/update_SOEPD/hazard_maps/active_faults/VFS/pasig.pdf

Related Links :
http://www.interaksyon.com/business/63559/bgc-gas-pipes-sitting-atop-fault-lines-up-geologist-says