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A major tsunami
earthquake occurred in the Indian Ocean, to the south-west of
Java, Indonesia, on 17
July 2006 at 15:19
PM local time. The earthquake had a
magnitude of Mw=7.7
and was felt at many places on the island of Java.
A damaging local tsunami was observed along the south coast
of Java and as a precautionary measure people were evacuated from
coastal areas of countries as far as India.
The earthquake
was centred 191 kms S of Bambayang
(Java), Indonesia,
211 kms S of Sindangbarang (Java), Indonesia,
223 kms NE of The Settlement (Christmas Island), Australia,
265 kms SW of Cilacap (Java), Indonesia,
271 kms S of Bandung (Java), Indonesia,
357 kms SSE of Jakarta (Java), Indonesia,
633 kms WSE of Surabaya (Java), Indonesia.
The earthquake
was felt throughout the island of Java including at Bandung,
Cilacap & Yogyakarta. It was also felt in parts of West Java
Province, especially from Pangandaran beach up to Cilacap and
Kebumen Districts in Central Java Province.
In the Indonesian capital, Jakarta, occupants of high-rise
buildings felt tremors for 30-60 seconds and some buildings were
vacated. The mainshock was followed by several strong aftershocks
including a Mw=6.2 at 09:13 UTC, a Mw=6.0 at 10:09 UTC and a
Mw=6.3 at 15:45 UTC.
This earthquake
produced a destructive local tsunami along the south coast of
Java. 668 people were confirmed dead
with another 65 listed as missing as of 5
August 2006. The Pacific Tsunami Warning Centre issued a
"Tsunami Watch" for Indonesia & Australia immediately after the
earthquake. The low shaking intensities along the coast of West
Java, including at Pangandarang, during the main earthquake did
not result in alarm and therefore many people did not perceive the
imminent danger of a tsunami. The only warning sign was what
eyewitnesses described as a withdrawal of the sea up to
1,500-metres that was then followed 30-minutes later by a tsunami
with waves estimated to have been up to 6-metres high. Many
buildings were damaged, including several hotels, at Pangandarang.
The tsunami was also observed at Sindangbarang in West Java and on
Samas Beach in Yogyakarta. The 2x300 MW powerplant at Cilacap was
also affected by the tsunami and despite attempts to keep it
functional, it had to be shut down.
It was also recorded on
Bali in Indonesia and in the Cocos Island, Australia. A tide gauge
on Christmas Island, Australia, recorded a wave that was
60-centimetres in height. Warnings & advisories were issued by many
countries around the Indian Ocean. The residents of the Australian
Christmas Island had 20-minutes prior warning to head for higher
ground. In India, beaches & coastal areas were vacated along the
east coast including Marina Beach in Chennai while the Andaman &
Nicobar islands were placed on high alert. Alerts were also sounded
at Kakinada, Srikakulam & West Godavari in Andhra Pradesh and at
Digha & the Sankarpur Harbour in West Bengal. In Sri Lanka, TITLEhough
no warnings or watches were in effect, residents were urged to be
cautious for unusual but minor tidal fluctuations.
The mechanism of this
earthquake is thought to have been similar to an Mw=7.6 event off
Nicaragua in 1992 and an Mw=7.8 event off East Java in 1994. Both
produced disproportionate lower levels of ground shaking in
comparison to their magnitudes. |
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References
01)
National
Earthquake Information Centre (NEIC), Golden, USA.
02)
Harvard Centroid Moment Tensor Solution (HRV), Harvard, USA.
03) Macroseismic information has been compiled by
the ASC from reports by local media and local NGO personnel.
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