Posted on November 4th, 2014

Our Changing Landscape – The 2013 Bohol Earthquake

In this monthly feature, we span the globe to examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 5 billion square kilometers of data. This month, we look at the damage done by the 2013 Bohol earthquake around Tubigon, Philippines.

The RapidEye Constellation

RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers daily revisits to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a starting cost of $1.28 per square kilometer for all five spectral bands – academics do receive discounts. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape.

The 2013 Bohol Earthquake

RE_Anime_2013_Bohol_EarthquakeClick on the image above to see an animation of 5-meter natural color RapidEye imagery collected over Tubigon, Philippines on July 25, 2013, October 19, 2013 (right after the earthquake) and February 28, 2014. Sometimes in failure there is success in that in this imagery, very little damage from the earthquake can be detected visually even just several days out from the disaster. This suggests that most of the damaged structures in a smaller community will not be detected at 5-meter resolution. In the July 2013 and then the February 2014 images, you can see that the colors of the structures in Tubigon have changed in many locations, suggesting some rebuilding following the disaster. (Images Courtesy: RapidEye)

On October 15, 2013 at 8:12AM, a magnitude 7.2 earthquake rocked the Pilipino island province  of Bohol with an intensity equal to 32 Hiroshima atomic bombs. The epicenter of the quake was located close to the center of the island, about 2 kilometers (km) southeast of Carmen, Bohol, and then 12-km below ground. As of 1PM the next day, the quake resulted in 885 aftershocks, with at least 15 of them felt by the local population. The strongest shaking was recorded in Tagbilaran City which is on the southwest corner of the island. Bohol has a long history of seismic activity, in fact it is one of the most active locations in the Philippines. A multitude of faults crisscross the island, including the East Bohol Fault which was originally deemed responsible for the 2013 earthquake; however, a team of academics discovered a new fault, the North Bohol Fault, which they believe was actually the guilty party. The Bohol earthquake was powerful enough to shift the island 55 centimeters due west and then create some 500 meters of new shoreline.

The 2013 Bohol earthquake was categorized as Very High Intensity (a Level VII quake on a scale that goes up to X) according to the Mercalli intensity scale which measures the affects of the event on the local population and infrastructure. As a Level VII quake, the damage it caused was not localized to the epicenter, rather there were wide areas along the north and northwest of Bohol island that were devastated. In all, some 200,000 residents were impacted or about 40,000 households, leaving 209 dead, 877 injured and 8 missing in Bohol province.

One of the hardest hit cities on Bohol was Tubigon which is located on the central west coast of the province. Some 8,000 families or 40,000 people were in need of assistance following the 2013 earthquake. 30% of the houses in the town were condemned which equated to 2,368 structures, 681 of them collapsed and 1,558 damaged beyond repair. Most of the structures that were impacted by the quake experience complete failure and the material did not make a difference as both masonry buildings and those made with local materials were equally impacted. Bridges, roads and even ports were heavily damaged so relief efforts were hampered by the lack of access to the region. Further, there was no electricity nor water for drinking purposes and local hospitals were over-whelmed, offering minimal treatments in open air tents. As the final straw that broke the camel’s back, Bohol was hit by Super Typhoon Haiyan on November 7th, sending 40,000 Bohol residents to evacuation centers.

If you would like to find out more about using RapidEye for your academic studies, engineering projects or any landscape analysis, let us know at sales@apollomapping.com or (303) 993-3863.

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