Strong Quakes, Kermadecs and Java

A strong, deep earthquake struck the Kermadec Islands this morning, ten hours after a damaging quake struck the Indonesian island of Java.

Thursday 3rd September 2009

A magnitude 6.2 earthquake struck the Kermadec Islands at 6 o’clock this morning. The quake was located 95 km west of Raoul Island (245 km north of L’Esperance Rock) at a depth of 260 km.

The earthquake follows a magnitude 6.6 event further north mid-way between Tonga and Samoa on Monday morning. The Kermadec quake was located deep within the Pacific plate while the Samoa/Tonga event was a shallow earthquake located within the Pacific tectonic plate, very close to the boundary with the Tonga Microplate.

Another earthquake of note struck at 7:55 New Zealand time last night, when a magnitude 7.0 earthquake struck 95 km south-south-west of Bandung, on the island of Java, Indonesia. The quake was 50 km deep and caused serious damage in smaller towns near the epicentre. More than 40 deaths have occurred and several hundred are reported injured.

Initial reports put the Java quake at between magnitude 7.0 and 7.6 and a tsunami was feared. The quake was an undersea event off the southern coast of Java and some previous quakes in this area have generated tsunami waves. However, those events were shallower and stronger than last night’s earthquake. Communication with some coastal communities in Java is still difficult, and landslides into the sea may have generated local waves in harbours. Sea gauges in the general area have not detected changes in sea level at distances from the earthquake epicentre.

Peculiar to last night’s earthquake is the lack of aftershocks from a large earthquake. Only one aftershock of magnitude 4.9 has been reported in the twelve hours since the main event. It has been suggested that because the earthquake occurred within a tectonic plate rather than close to a boundary, that few aftershocks will result.

The three earthquakes are not directly linked but represent the activity that occurs along the active plate boundaries in the Pacific and Indian Ocean areas.

[Compiled from data supplied by the U.S. Geological Survey and its contributing agencies.]

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