Directions: In this part, you will have 15 minutes to
go over the passage quickly and answer the questions on Answer Sheet
1. For questions 1-4, mark Y (for YES)
if the statement agrees with the information
given in the passage; N (for NO)
if the statement contradicts the information given in the passage;
NG (for NOT GIVEN) if the information is not given in the
passage. For questions 5-10, complete the sentences with the
information given in the passage. Tsunami Up until
December of 2004, the phenomena of tsunami was not on the minds of most of the
world’s population. That changed on the morning of December 24, 2004 when an
earthquake of moment magnitude 9.1 occurred along the oceanic trench off the
coast of Sumatra in Indonesia. This large earthquake resulted in vertical
displacement of the sea floor and generated a tsunami that eventually killed
280,000 people and affected the lives of several million people. Although people
living on the coastline near the epicenter of the earthquake had little time or
warning of the approaching tsunami, those living farther away along the coasts
of Thailand, Sri Lanka, India, and East Africa had plenty of time to move to
higher ground to escape. But, there was no tsunami warning system in place in
the Indian Ocean, and although other tsunami warning centers attempted to
provide a warning, there was no effective communication system in place.
Unfortunately, it has taken a disaster of great magnitude to point out the
failings of the world’s scientific community and to educate almost every person
on the planet about tsunami. How Tsunamis Are
Generated There is an average of two
destructive tsunamis per year in the Pacific basin. Pacific wide tsunamis are a
rare phenomenon, occurring every 10-12 years on the average. Most of these
tsunamis are generated by earthquakes that cause displacement of the seafloor.
Earthquakes cause tsunami by causing a disturbance of
the seafloor. Thus, earthquakes that occur along coastlines or anywhere beneath
the oceans can generate tsunami. The size of the tsunami is usually related to
the size of the earthquake, with larger tsunami generated by larger earthquakes.
But the sense of displacement is also important. Tsunamis are generally only
formed when an earthquake causes vertical displacement of the seafloor. The 1906
earthquake near San Francisco California had a Richter Magnitude of about 7.1,
yet no tsunami was generated because the motion on the fault (断层) was
strike-slip motion with no vertical displacement. Thus, tsunami only occur if
the fault generating the earthquake has normal or reverse displacement. Because
of this, most tsunamis are generated by earthquakes that occur along the
subduction boundaries of plates, along the oceanic trenches. Since the Pacific
Ocean is surrounded by plate boundaries of this type, tsunamis are frequently
generated by earthquakes around the margins of the Pacific Ocean.
Examples of Tsunami Generated by Earthquakes
May 22, 1960-A moment magnitude 9.5 earthquake occurred along the
subduction zone off South America. Because the population of Chile is familiar
with earthquakes and potential tsunami, most people along the coast moved to
higher ground. 15 minutes after the earthquake, a tsunami with a run-up of 4.5 m
hit the coast. The first wave then retreated, dragging broken houses and boats
back into the ocean. Many people saw this smooth retreat of the sea as a sign
they could ride their boats out to sea and recover some of the property swept
away, by the first wave. But, about 1 hour later, the second wave traveling at a
velocity of 166 km/hr crashed in with a run-up of 8 m. This wave crushed boats
along the coast and destroyed coastal buildings. This was followed by a third
wave traveling at only 83 km/hr that crashed in later with a run-up of 11 m,
destroying all that was left of coastal villages. The resulting causalities
listed 909 dead with 834 missing. In Hawaii, a tsunami warning system was in
place and the tsunami was expected to arrive at 9:57 AM. It hit at 9:58 AM and
61 people died, mostly sightseers that wanted to watch the wave roll in at close
range (obviously they were too close). The tsunami continued across the Pacific
Ocean, eventually reaching Japan where it killed an additional 185 people.
Prediction and Early Warning
For areas located at great distances from earthquakes that could
potentially generate a tsunami there, is usually plenty of time for warnings to
be sent and coastal areas evacuated, even though tsunami travels at high
velocities across the oceans. Hawaii is a good example of an area located far
from most of the sources of tsunami, where early warning is possible and has
saved lives. For earthquakes occurring anywhere on the subduction margins of the
Pacific Ocean there is a minimum of 4 hours of warning before a tsunami would
strike any of the Hawaiian Islands. The National Oceanic
and Atmospheric Administration (NOAA) has set up a Pacific warning system
for areas in the Pacific Ocean, called the Pacific Tsunami Warning Center. It
consists of an international network of seismographic stations, and tidal
stations around the Pacific basin that can all send information via satellite to
the Center located in Hawaii. When an earthquake occurs somewhere in the region,
the Center immediately begins to analyze the data looking for signs that the
earthquake could have generated a tsunami. The tidal stations are also
monitored, and if a tsunami is detected, a warning is sent out to all areas on
the Pacific coast. It takes at least 1 hour to assimilate all of the information
and issue a warning. Thus for an average velocity of a tsunami of 750 km/hr, the
regional system can provide a warning sufficient for adequate evacuation of
coastal areas within 750 km of the earthquake. In order
to be able to issue warnings about tsunami generated within 100 to 750 km of an
earthquake, several regional warning centers have been set up in areas prone to
tsunami generating earthquakes. These include centers in Japan, Kamchatka,
Alaska, Hawaii, French Polynesia, and Chile. These
systems have been very successful at saving lives. For example, before the
Japanese warning system was established, 14 tsunamis killed over 6000 people in
Japan. Since the establishment of the warning system 20 tsunamis have killed 215
people in Japan. Tsunami Safety Rules A strong earthquake felt in a low-lying coastal area is
a natural warning of possible, immediate danger. Keep calm and quickly move to
higher ground away from the coast. A tsunami is not a
single wave, but a series of waves. Stay out of danger until an "ALL CLEAR" is
issued by a competent authority. Approaching tsunamis
are sometimes heralded by noticeable rise or fall of coastal waters. This is
nature’s tsunami warning and should be heeded. A small
tsunami at one beach can be a giant a few miles away. Do not let modest size of
one make you lose respect for all. Never go down to the
beach to watch for a tsunami WHEN YOU CAN SEE THE WAVE YOU ARE TOO CLOSE TO
ESCAPE. Tsunami can move faster than a person can run
Homes and other buildings located in low lying coastal areas are not safe.
Do NOT stay in such buildings if there is a tsunami warning.
The upper floors of high, multi-story, reinforced concrete hotels can
provide refuge if there is no time to quickly move inland or to higher ground.
If you are on a boat or ship and there is time, move
your vessel to deeper water (at least 100 fathoms). If it is the case that there
is concurrent severe weather, it may be safer to leave the boat at the pier and
physically move to higher ground. Damaging wave activity
and unpredictable currents can affect harbor conditions for a period of time
after the tsunami’s initial impact. Be sure conditions are safe before you
return your boat or ship to the harbor. Stay tuned to
your local radio, marine radio, NOAA Weather Radio, or television stations
during a tsunami emergency--bulletins issued through your local emergency
management office and National Weather Service offices can save your life.
You may take shelter on upper floors of high, multi-story, reinforced concrete hotels when it is impossible to______.