26 December 2004

Earthquake near Sumatra - location map and seismic charts - [updated 28Mar05]

28Mar05 Added recent earthquake information:
1. updated area map showing location of both events
2. Seismic Plot from Sydney, BC - compare with 26Dec05
3. Seismic Plot from Olympic Penninsula - compare with 26Dec05
4. a second animation of the 26Dec05 Tidal Wave [pending]

14Feb05 Added article from Royal Navy [UK] with images of ocean floor
03Jan05 Added link to Sri Lanka Government Tsumani Page &
Tsunami Blog

30Dec04 Update: Satellite Imagery from UNO added.

How can you help? Donate cash to a registered NGO development organization of your choice. Cash allows relief workers to buy what is needed from suppliers near the disaster area and start rebuilding the local economy.

List of Vancouver based organizations that are involved with
International Development from The Red Book online.

Link to news on relief efforts from ReliefWeb

Link to Sri Lanka National Disaster Management Centre

Link to The South-East Asia Earthquake and Tsunami Blog

Living on the West Coast, I am always interested in earthquakes occuring in the Pacific Rim, because there will be a Big One here someday.

BC Provincial Emergency Program


The Eathquake

25 December 4:58 p.m. PST: A magnitude 8.9 earthquake struck just off the coast of Sumatra (at 06:58 a.m. Dec. 26 Sumatra time). This earthquake, the world's largest quake in nearly 40 years, was felt in Sumatra, Bangladesh, India, Malaysia, Myanmar, Singapore and Thailand. There are reports of significant damage in the epicentral area, and many people were reported killed in Sri Lanka by a tsunami generated by this earthquake. There is no tsunami threat to Canada's west coast.

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Distance from epicenter:
255 km (160 miles) SSE of Banda Aceh, Sumatra, Indonesia
315 km (195 miles) W of Medan, Sumatra, Indonesia
1260 km (790 miles) SSW of BANGKOK, Thailand
1590 km (990 miles) NW of JAKARTA, Java, Indonesia

Detailed tectonic map of the area provided by USGS

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Comparison Map 28 March 2005

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Preliminary Earthquake Report
U.S. Geological Survey,
National Earthquake Information Center
World Data Center for Seismology, Denver

The devastating megathrust earthquake of December 26, 2004, occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate. The India plate begins its descent into the mantle at the Sunda trench, which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast.

In the region of the earthquake, the India plate moves toward the northeast at a rate of about 6 cm/year relative to the Burma plate. This results in oblique convergence at the Sunda trench. The oblique motion is partitioned into thrust-faulting, which occurs on the plate-interface and which involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers to the east of the trench and involves slip directed parallel to the trench. The December 26 earthquake occurred as the result of thrust-faulting.

Preliminary locations of larger aftershocks following the megathrust earthquake show that approximately 1200 km of the plate boundary slipped as a result of the earthquake. By comparison with other large megathrust earthquakes, the width of the causative fault-rupture was likely over one-hundred km. From the size of the earthquake, it is likely that the average displacement on the fault plane was about fifteen meters. The sea floor overlying the thrust fault would have been uplifted by several meters as a result of the earthquake. The above estimates of fault-dimensions and displacement will be refined in the near future as the result of detailed analyses of the earthquake waves.

The world's largest recorded earthquakes have all been megathrust events, occurring where one tectonic plate subducts beneath another. These include:

the magnitude 9.5 1960 Chile earthquake, the magnitude 9.2 1964 Prince William Sound, Alaska, earthquake, the magnitude 9.1 1957 Andreanof Islands, Alaska, earthquake, and the magnitude 9.0 1952 Kamchatka earthquake. As with the recent event, megathrust earthquakes often generate large tsunamis that cause damage over a much wider area than is directly affected by ground shaking near the earthquake's rupture.
Source: http://earthquake.usgs.gov/recenteqsww/Quakes/usslav.htm

Seismic plot from Sidney, BC [30 minutes]

The plot below shows seismic data from the past 24 hours, as received at PGC and enhanced to show major earthquake events from all over the world. This special "Long Period" plot is optimized for displaying very low frequency vibrations that travel over long distances from earthquake sites. Each horizontal line shows 30 minutes of data. On the left side of a plot is the starting time for each line in Universal Time. On the right side is the starting time in PGC Local Time (PST or PDT).

Data in BLACK starts "On the Hour". Minutes past the hour are on the BLACK scale (00 to 30).
Data in BLUE starts "On the Half-hour". Minutes past the half-hour are the BLUE scale (30 to 60).


A different chart overlapping earthquake time and showing aftershocks:


Current status


Seismic plot from Port Angeles, WA [10 minutes]
this gives detail of seismic activity over a shorter timeframe



Event: 2004/12/26 00:58:50.7
Source: SPYDER®
Click on the "Seismic Monitor" link

Station: PALK - Pallekele, Sri Lanka ~1650 km from epicenter
Network: II - Global Seismograph Network (GSN - IRIS/IDA)
Lat: 7.27 Lon: 80.70 Elev: 460.00
Event Name: 20041226_005850.7.spyder
Available Channels: BH1,BH2,BHE,BHN,BHZ,BLE,BLN,BLZ,LH1,LH2,LHZ
Available Locations: 00,10




primary (P-) wave - earthquake body wave that travels fastest and advances by push-pull mechanism. Also known as longitudinal, compressional, or P wave.

S -Wave - a transverse seismic wave produced by shearing motion. S-waves are so called because they are the second set of waves to arrive from an earthquake.

Interesting coincidence:

2003 December 26 01:56:52 UTC
**1 year and 58 minutes to the day!!**

...and Effect


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Image found at Digitalcatharsis apparently from the NOAA

Area affected [large image 1600 x 1100] opens in a new window

From UNOSAT - satellite imagery for all

More Satellite Images from DigitalGlobe


Navy survey ship scans tsunami earthquake zone
10.02.05 11:43

A Royal Navy survey ship has provided scientists with the first
detailed images of the sea bed which triggered the devastating
Boxing Day tsunami in the Indian Ocean.

Ocean survey vessel HMS Scott was in the western Indian Ocean
when a massive earthquake struck almost 100 miles off the coast
of Sumatra, sending a massive pulse of water which destroyed
waterside communities around the edge of the ocean.

She would have ridden over the wave at some point on that day,
but because of the depth of water in the region near Madagascar
her ship’s company of 42 would not have felt it – the wave only
poses a threat when it reaches shallow water and rears up into
the huge wall of water which terrified communities thousands
of miles apart.

With the co-operation of the Indonesian government, Scott is
spending almost three weeks above the epicentre of the quake,
obtaining three-dimensional images of the sea bed using
state-of-the-art sonar and computer equipment.

At depths of up to 5,000 metres, Scott found evidence of massive
disruption, with faults many kilometers long and several hundred
metres high associated with landslides as the Burma and Indian
tectonic plates collided, causing a huge release of energy which
was transferred by the ocean itself to the countries bordering the
Indian Ocean, with Indonesia, Thailand, India and Sri Lanka being
particularly hard-hit.

Current estimates are that more than a quarter of a million people
died when the waves swept ashore. Scott was on site exactly a month
after the quake, allowing scientists to get a good look at the scene
before sediment and the action of the sea starts to mask the scars.

The images are low-resolution – they will be enhanced using powerful
analytical computers in the weeks to come – and the colour-coding
shows depths in the ocean.

The area is not one which has been well-charted in recent times – i
t is believed most surveys date back to the early quarter of the 20th
century, and some as far back as the 1880s.

Scott, which is part of the Devonport-based Hydrographic and
Surveying Squadron, carried with her experts from the British
Geological Survey and the Southampton Oceanography Centre.

It is hoped the information gleaned by Scott can be put to good
use in determining danger signs for future earthquakes and
tsunami, and will also figure in investigations into early-warning

More images:

28 March 2005 - Earthquake / Aftershock

Monday, March 28, 2005

A great earthquake occurred at 16:09:36 (UTC) on Monday, March 28, 2005. The magnitude 8.7 event has been located in NORTHERN SUMATRA, INDONESIA. (This event has been reviewed by a seismologist.)


Date-TimeMonday, March 28, 2005 at 16:09:36 (UTC)

Monday, March 28, 2005 at 11:09:36 PM

Location2.065°N, 97.010°E
Depth30 km (18.6 miles) set by location program

205 km (125 miles) WNW of Sibolga, Sumatra, Indonesia
250 km (155 miles) SW of Medan, Sumatra, Indonesia
535 km (330 miles) WSW of KUALA LUMPUR, Malaysia
1410 km (880 miles) NW of JAKARTA, Java, Indonesia

Felt Reports

At least 290 people killed, 100 injured and 300 houses destroyed on Nias. Extensive damage on Simeulue. Felt in Indonesia, Malaysia, Singapore and as far north as Bangkok, Thailand.

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