An earthquake of 5.5 magnitude struck the northern Philippine province of Isabela at 9:08 p.m. on May 21st which was followed by 8 more earthquakes or aftershocks within 12 hours after the first quake. This is according to the Philippine Institute Volcanology and Seismology's (Phivolcs) earthquake bulletin.
The map shows the epicenter (red dot) of the quakes | Source: PhivolcsThe initial quake was felt at the following intensities in the following areas:
Intensity V - Ilagan, Isabela
Intensity IV- Tuguegarao City, Cagayan; Penablanca, Cagayan; Quirino Province; Tumawini, Isabela; Baler, Aurora
Intensity II - Baguio City; Tabuk, Kalinga
All the temblors were of tectonic origin with Ilagan, Isabela as a common epicenter.
Here are the time and magnitude of each aftershock:
21 May 2011 - 10:12 PM, Magnitude 3.4
21 May 2011 - 10:20 PM, Magnitude 2.4
22 May 2011 - 12:19 AM, Magnitude 2.1
22 May 2011 - 12:52 AM, Magnitude 2.3
22 May 2011 - 01:44 AM, Magnitude 3.3
22 May 2011 - 02:19 AM, Magnitude 2.3
22 May 2011 - 03:48 AM, Magnitude 2.6
22 May 2011 - 09:25 AM, Magnitude 2.4
Six more quakes jolted other Philippine provinces on May 21st.
There have been no reports of damage from the quakes as of present time.
Multiple earthquakes in one day is not unusual in the Philippines since it lies on the Pacific Ring of Fire where volcanic and seismic activities are more frequent.
Isabela is quite seismically active nowadays... last week, another quake occurred...
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