Island Watch – Tonga Aftershocks

Aftershocks of the major earthquake near Tonga on May 4th (NZ Time) rapidly abated in frequency and strength over the following three weeks.

The magnitude 7.9 earthquake struck near Tonga at 3:27 a.m. on May 4th New Zealand Time (15:27 on May 3rd U.T.).

During the following week, the US Geological Survey reported 66 earthquake events of magnitude 4 or more within 200 km of the epicentre.

During the second week, earthquake rates rapidly dropped to 14 and only 8 events were reported during the third week.

Earthquakes within 200 km of the major quake’s epicentre can be summarised as follows:
Week 1: mag. 6 (2), mag. 5 (19), mag. 4 (45), total 66
Week 2: mag. 6 (1), mag. 5 (3), mag. 4 (10), total 14
Week 3: mag. 6 (0), mag. 5 (1), mag. 4 (7), total 8

The magnitude of the main earthquake has been finalised at mag. 7.9 and its depth at 55 km.

The reason for the rapid abatement of activity is unclear.

The only event reported so far during the 4th week since the main shock (which ends on Thursday morning) was a magnitude 5.4 event which struck at 10:35 this morning.

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