The Sumatra quake as recorded by a seismograph in Perugia, Italy
Key to box
colours
3.800
Data recorded
by seismograph
Time of event
00.58 GMT
001
UMBER
ETIN N ING CENTER
N
I BULL
TSUNAM TSUNAMI WAR 4
00
C
AII
PACIFI ST 25 DEC 2
OF HAW
H
STATE
0315PM
N THE
I
E
N
S
I
N
EFE
BULLET
IVIL D
ATION
TO - C
INFORM
E
UNAMI
S
T
H THES
T
I
W
T
ED
SUBJEC
OCCURR
S
A
H
E
ERS
THQUAK
04
AN EAR ARY PARAMET
DEC 20
IN
HST 25 AST
PRELIM
9
E
25 PM
7
0
.
5
9
E
TIM
UMATRA
ORTH
ORIGIN TES - 3.4 N OAST OF N S
C
NA
W
I
D
F
R
F
O
O
O
C
ON
MOMENT
LOCATI E
- 8.0
*****
UD
******
MAGNIT
*****
To the west of Sumatra the IndianAustralian tectonic plate slips 90cm
under the Burma plate – after 150
years of no movement. The
enormous release of energy triggers
a surge of powerful tsunami radiating
across the Indian Ocean at speeds of
up to 500mph
2.533
******
******
******
*****
******
1.267
01.15 GMT
Officials at the Honolulu-based
Pacific Tsunami Warning Center issue
standard bulletin warning of ‘event'
initially recorded at magnitude 8 off
the northern coast of Sumatra. The
magnitude is later revised to 9
01.18
01.14-01.30
First aftershock recorded
Huge waves crash on to the shoreline
of the Thai island of Phuket and the
Aceh province of Indonesia.
Within two hours, the tsunami has hit
the coasts of India and Sri Lanka,
eventually travelling as far as the
Maldives and Somalia
**
******
******
mm 0
S-P interval
Because S-waves travel more slowly
than P-waves, the gap between the
arrival times of the first P and S
waves becomes progressively larger
according to the distance of the
seismograph from the quake. The
S-P interval is used to determine
distance of the seismograph from
the epicentre. Distance
determinations from three,
geographically well-spaced
seismographs locate its precise
position. The interval recorded here
is 10mins 12secs. The distance
worked out by this seismograph is
5,692 miles
1.267
Vertical
movement in
millimetres of
ground surface
P-wave
S-wave
Primary waves travel through the
body of the Earth at speeds of up to
40,000km/hour. They are waves that
involve the crust being pushed and
pulled in the direction of travel, in a
manner similar to an engine shunting
a line of railway wagons. Because
they travel fastest, P-waves are the
first to arrive at a seismograph
2.533
3.800
00:56:35 GMT
00:35
04:35
CHINA
INDIA
BANGLADESH
INDIA
Secondary waves travel at only about
half the speed of P-waves. They are
also only able to travel through solid
rock and cannot pass through the
Earth’s molten outer core. S-waves
cause the crust to move up and
down. The S-waves recorded here
arrived at 1.08GMT
Dhaka
Calcutta
BURMA
Sitwe
ANDHRA
PRADESH
SRI
LANKA
Fault line
2
Pondicherry
Trincomalee
nutes
mi
utes
4 min
Colombo
INDIAN
OCEAN
inutes
3m
KERALA
THAILAND
Indo-Australian Plate
Madras
TAMIL
NADU
Rangoon
Burma Plate
Bangkok
ANDAMAN Ł
ISLANDS
NICOBARŁ
ISLANDS
Phuket
Banda
Aceh
ACEH
Meulaboh
Penang
MALAYSIA
SUMATRA
Epicentre
INDONESIA
Padang
Time taken for seismic
P-waves to travel
500 miles
08:35
Surface waves
Surface waves travel most slowly of
all as they are confined to the outermost crust of the earth. They are the
most destructive of all seismic waves
and cause sideways shaking as well
as a rolling motion similar to water
waves
12:35
Shock wave progress
Seismic waves moving at a rate of
2km a second. First phase involves a
rupture about 400km long and
100km wide and just 30km beneath
the sea bed.
Nine quakes in excess of magnitude
six recorded in next 24 hours and
more than 80 occur by January 2,
2005.
16:35
20:35
24:35
28:35
32:35
Amplitude
The amplitude of a seismic wave is
its peak-to-trough height divided by
two. On a seismogram it provides a
measure of the intensity of ground
motion, which is often shown in
millimetres. Amplitude tends to
increase from P-waves, through Swaves to surface waves
36:35
Elapsed time from
start of quake
40:35
Source: www.infoeq.it