According to the USGS, the August 5, 2018, M 6.9 earthquake in Pulau Lombok, Indonesia, occurred as the result of shallow thrust fault on or near The Flores Back Arc Thrust. At the latitude of this earthquake, the Sunda and Australia plates converge in a north-south direction at a rate of about 70 mm/yr. In the region surrounding this earthquake, there have been six other events of M 6.5 or larger over the previous century. Four of these are likely to have occurred on the back arc thrust system; a M 6.5 event in the Bali region to the west of Lombok in July 1976, and three events of M 6.5, M6.5, and M 6.6 in the Sumbawa region to the east of Lombok in November 2007 and November 2009. The Sumbawa earthquakes were associated with several deaths, hundreds of injuries, and hundreds of houses being destroyed.

The earthquake registered 7. Local media have reported that Indonesian authorities briefly issued a tsunami warning which was later cancelled.

A 13cm wave was recorded on the western side of Lombok, which is too small to have significant impact.

At no stage was Australia considered to be under threat, according to the Joint Australian tsunami Warning Centre (JATWC).  JATWC as a Tsunami Service Provider for the Indian Ocean also provided threat information to warning authorities in the region.

JATWC will soon be releasing a new webpage which displays real-time earthquake information and tsunami warning status provided to JATWC by the Indian Ocean tsunami warning authorities.

Our results draw a new kinematic framework for active deformation in the eastern Sunda-Banda Arc, highlighting the need to reconsider the level of seismic hazard there.

Several of the active faults identified here directly threaten socioeconomic assets vital to Indonesia. The Kendeng thrust passes through the southern outskirts of Surbaya, Indonesia’s second largest city with a population of over 2.5 million, and traverses a 300 km length of East Java, with a population density of over 800 people per square kilometer. The Semau Fault skirts the city of Kupang, the main commercial centre of Nusa Tenggara with a population of around 500,000.

Finally, earthquakes along the back-arc thrust beneath the sea floor extending 1700 km from eastern Java to Timor could generate regional tsunamis threatening the coastlines of the Flores Sea. Further studies, including earthquake, geodetic, and paleoseismic, should be undertaken to better understand these threats.

The magnitude 7 earthquake that struck Lombok Island, Indonesia, last night occurred just below the Island's northern coast. Its location is very close to the magnitude 6.4 earthquake that occurred one week ago, and its faulting mechanism appears to be very similar.

These were both shallow earthquakes, and both caused considerable damage. But last night's earthquake was 4 times larger and released much more energy. It caused strong shaking throughout Lombok and Bali and was even felt in eastern Java.

Professor Elders is available today to discuss the below and similar, including:

*    Why do earthquakes occur in this part of Indonesia?

*    Is the earthquake likely to be followed by further seismic events or an aftershock?

*    Does the earthquake have the potential to generate a tsunami or significantly impact tides? 

*    Was the earthquake felt in Australia?

*    Is there a risk to other tourist-populated areas of Indonesia of a similar or related earthquake?

The magnitude 6.9 Loloan, Indonesia earthquake was a reverse faulting earthquake at a depth of 31km.

In this area the Sunda plate to the north subducts beneath the Indonesian Arc, and the mechanism of the earthquake is consistent with reverse-faulting on the Indonesian Arc thrust.

The Pacific Island arc from Samoa to Indonesia is one of the most seismically active regions on Earth, and earthquakes of this size are not unusual. In the region within about 500km of the epicentre there have been at least 15 earthquakes of magnitude 6.5 and above in the last 10 years.

Earthquakes of this size will produce significant aftershock activity. However, plate interface earthquakes tend to have less vigorous aftershock sequences than shallow crustal earthquakes of comparable size.