Continuous creep dislocation of the valley fault system in Metro Manila, Philippines
|Location||International Geological Congress,oslo 2008|
|Author||Kinugasa, Yoshihiro۱; Papiona, Kathleen۱; Rimando, Rolly۲; Kurita, Katsumi۳|
|Holding Date||04 October 2008|
The Western Valley Fault (known also as the Marikina Fault) is a north-south trending active fault in the Metro Manila district, Philippines. Buildings and road pavement are damaged by vertical displacement of the ground where the southern segment of the fault passes through.
There are two possible hypotheses for the mechanism of the continuous creep dislocation of this Western Valley Fault. One is excess withdrawal of the underground water due to rapidly growing the urban area of the city and therefore demanding substantial amount of water supply. The other one is tectonic. Even though we have no certain evidences to support either hypothesis, if it is due to excess withdrawal of the underground water, such a creep dislocation may occur along other faults in rapidly growing urban areas and may cause damages to the buildings and other infrastructures near by the fault.
To monitor the movement of the fault, repeated leveling surveys across the fault has been carried on since September 1999 periodically. Since there has been no horizontal movement noticed, the survey method follows a simple leveling survey using an electronic digital level and bar-code leveling staff. Overall accuracy is estimated to be 2-3mm. Repeated survey intervals were once in every three month at the beginning, and now twice a year.
Though we set up eight survey lines at five locations, two survey lines at one location had been lost due to renovation of the ground. Later, in 2005, three additional survey lines have been set up.
Three survey lines show no creep dislocation even though fault scarplets and an echelon cracks on the pavement are visible. Until the recent survey done in December 2007, six survey lines out of nine show continuous creep dislocation. Trace of each fault is not changing throughout the survey period, and width of the deformation zone associated with each fault is very limited ranging from 1.5 to 6.1 meters. The average slip rates of these six survey lines since the beginning of the survey ranges 0.99cm/y to 2.13cm/y.