A moderate earthquake measuring 5.9 magnitude on the Richter scale hit the northern Philippines but caused no damage or injuries. The Philippine Institute of Volcanology and Seismology said the tremor struck at the wee hours of Tuesday and was centered 19 miles (30 kilometers) under the sea about 22 miles (35 kilometers) off Iba township in Zambales province. The institute has recorded at least three aftershocks with magnitudes 2.8 to 4.0. It says the quake was generated by the Manila Trench that runs north to south off the western coast of the main island of Luzon. The Philippines is within the Pacific Ring of Fire where earthquakes and volcanic activity is common.