Calatagan Is Batangas’ 2012 Earthquake Capital

There were a total of 52 earthquakes that occurred in the Province of Batangas from 1 February 2012 to 1 February 2013. In other words, an earthquake occurred in the province roughly every seven days.

Of the 52 earthquakes, as many as 38 occurred in or close to the Municipality of Calatagan in Western Batangas. Another 7 occurred in or close to the Municipality of Nasugbu; 3 in or close to Batangas City; 2 in or close to the Municipality of Sto. Tomas; and 1 each in or close to the Municipalities of Calaca and Talisay.

LOCATION	FREQ.
Calatagan	38
Nasugbu	7
Batangas City	3
Sto. Tomas	2
Calaca	1
Talisay	1

Despite the seeming frequency, majority of the earthquakes would have occurred largely unnoticed. The most powerful quakes were those that occurred on 29 September 2012 in Calatagan with a magnitude of 5.2 and in Nasugbu on 23 November 2012 with a magnitude of 5.0.

Of the 52 earthquakes, only 13 registered a magnitude 4.0 or higher which would have been felt significantly. An earthquake of magnitude 4.0 or higher occurred on average every 32 days.

MAGNITUDE	FREQ.
Magnitude 1-1.9	2
Magnitude 2-2.9	20
Magnitude 3-3.9	17
Magnitude 4.4.9	11
Magnitude 5 and higher	2

The amount of shaking on the surface is influenced by the depth at which the earthquakes occur. The shaking is more intense if the earthquake is shallower.

Of the 52 quakes that occurred in Batangas, the shallowest occurred at a depth of only 4 kilometres in the Municipality of Sto. Tomas on 5 April 2012. Fortunately, the earthquake was a mere magnitude 2.6.

The deepest earthquake, meanwhile, occurred at a depth of 198 kilometres in Calatagan on 26 February 2012. The quake registered a magnitude of 2.7.

Although there were significantly more earthquakes in Calatagan than Nasugbu, those in Calatagan tended to be not as strong with an average intensity of 2.2 compared to Nasugbu’s average of 3.8.

The quakes in Calatagan, on the other hand, tended to be shallower with an average depth of 89 kilometres compared to Nasugbu’s average depth of 123 kilometres.

LOCATION	FREQ	AVE MAG.	AVE DEP
Batangas City	3	2.8	54
Calatagan	38	2.2	89
Nasugbu	7	3.8	123
Sto. Tomas	2	2.5	54

Data from PHILVOCS.

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