John Pazmino
 2005 July 5 
    'Earthquakes, tsunamis, and a modern journey into the center of 
the Earth' was presented by Dr Michael Wysession, Washington 
University, St Louis MO, on 30 June 2005 at American Museum of Natural 
History. Perhaps because it was a free public lecture, it filled its 
hall, Kaufmann Theater, to capacity with few empty seats left. 
    For me this talk was paired with one I and other NYSkiers heard on 
June 22nd. That was 'Future eruptions of Vesuvius' at Science, 
Industry, Business Library. I summarized that lecture for NYSkies in 
file 'vesuvius.txt'. 
    The talk was hosted by the Museum's Department of Earth and 
Planetary Sciences. It's agent noted that this is a taste of a new 
series of lectures starting in October 2005 about geophysics. He urged 
the audience to watch the Museum website and litterature for details 
when October rolls around. 
    Wysession first described the structure of the Earth as an iron 
core, blanketed by a mantle of melted rock, and skinned over by the 
solid rock crust. This crust extends above sea level as land but about 
3/4 of it, the Earth's surface, is covered by ocean. 
    The crust floats on the mantle and in remote eras was formed as 
separate tiles or plates. At one time these were gathered into one 
landmass, Pangea. Over the eons, the plates separated and migrated to 
align with the landmasses of today. This feature is continental drift 
or plate tectonics. 
    The plate boundaries collide here and there. In general, they are 
separating in the Atlantic Ocean and converging around the Pacific 
Ocean. The boundaries are NOT congruent with shorelines; they may be 
under the sea or within the land. 
    The crust is tens of kilometers thick. In area, they ranges from 
middle-size countries to major continents. The plates are named for 
the continent or ocean covering the greater fraction of their area. 
Plate collision
    Around the Pacific Ocean, the plates are pressing together. As 
they rub, they set up stresses in the rock. When the stress builds up 
and the plates slip, there is a movement of the surface, an 
earthquake. This situation prevails all around the Pacific rim, in 
Japan, Alaska, west Canada, west United States, west Mexico, west 
South America, south Pacific islands, north Australia, Indonesia, west 
Pacific islands, southeast Asia, eastern China. 
    In the US the most famous of boundaries is the San Andreas fault 
in California, where the North America and Pacific plates gnash. Land 
to the east on the fault line is on the North America plate. That to 
the west is on the Pacific plate. The relative motion between the two 
is evidenced in the offset alignments of roads and sheared structures 
that cross the fault. The gaps between the plates was long ago filled 
with loose sediment, shaping the topography of California today. 
    Here the North American plate and the Pacific plate slide 
laterally and lock together. When the stress finally breaks them free 
for a next advance along the boundary, California suffers an 
    The quake is typicly several kilometers under the ground. The 
geographic spot on the surface above this seat is the epicenter. it 
has the dame lat-lon as the underground quake. 
Other quakes
    Earthquakes can occur within a plate, like in the Mississippi 
valley. The cause here is the plate being buckled or wrinkled by 
pressure around its edges. Where the plate is weakest, the buckling 
can trigger earthquakes. 
    An other cause of earthquakes, minor ones, is relaxation of the 
crust after depression under the Ice Ages. The quakes around new York 
City or mostly of this type. It did, and can, suffer the stronger ones 
due to plate wrinkling.
 ------Volcanos are formed along plate frontiers where one plate is 
shoved under an other, as is the case around the Pacific. The lower 
plate melts, mixes with superheated water from the ocean, and becomes 
magna. This magma oozes upward by the tectonic pressure and breaks 
thru cracks and holes on the surface; you got a volcano. 
    Earthquakes occur at and around times of volcano eruptions by the 
bulk motion of the magma and shifting of mass under the ground. The 
onset of earthquake in volcano territory can precede an eruption, but 
not for sure. The magma may simply migrate around but not break the 
    The bulk of volcanos on Earth surround the Pacific Ocean as the 
'Ring of fire'. Altho many of the volcanos are dormant or extinct, 
other nearby are quite live. In some cases, like Mt St Helens, a 
presumably extinct volcano can suddenly revive.
    The prototypical pacific island is a tall volcano with culture and 
development on the shoreline at its base. many in the Caribbean are 
like this, too, from plate collisions there. 
    Mountains can be raised up by plate motions. The Rockies and Andes 
are the result of plates pressing together with the overburden pushed 
upwards. The Himalayans are the result of the India plate migrating 
north into the Asia plate. These mountains are still today building up 
several centimeters every year. Slips in the mountains here cause the 
earthquakes in west Chine, Nepal, north India, Pakistan. 
    Mountains can be formed thru the buckling process, like the 
Appalachians  Apparently the rock here is soft enough to yield under 
pressure and prevent strong buildup of stress. There are few strong 
quakes along the Appalachians. 
    Along the flanks of the India plate is the situation similar to 
California. The plate rubs sideways against the next one (forget the 
name) containing Indonesia. Both severe quakes and strong volcanos are 
frequent in and around Indonesia. 
Shock waves
    An earthquake is the sudden release of energy that sends shock 
waves thru the surrounding crust and mantle. These propagate the wave 
long distances, around the world. By tracking these waves, we can suss 
out the thickness and density of the mantle and core. The speed and 
deflection of the waves gives clue for the composition of these 
    Because the waves can bounce off of the core or deflect thru the 
mantle, there is a ''skip' effect. There are 'dead' zones around the 
quake center where there is little or no effect, yet farther away on 
the same radial line, strong motion is felt. 
    Eventually the waves die out by frictional losses, but they can 
endure, circulating around the world several times, for many days or 
weeks. Waves from small quakes are spent within minutes.
Atom bombs 
    Until the Cold War, earthquake stations to monitor the waves were 
far and few between. Most were at what ever convenient place in a 
college laboratory. One I remember is the long-gone seismograph in the 
lobby of Shepard Hall, City College of New York. Data were collected 
by drum recorders, with the paper bands stored for later inspection. 
    The Cold War made it essential to monitor underground shocks from 
atom bomb testing. The US set up dozens of bases, mostly 
circumscribing the Soviet Union. Because time was critical to evaluate 
any bomb explosion, electronic and automatic recording methods were 
developed, along with suitable alarms. As it turned out, the Soviet 
Union occupied so vast an area that the stations were deployed 
adequately on the globe to look after natural earthquakes. 
    The signature of an earthquake is quite different from that of a 
bomb blast. The bomb explodes at one point for an instant. A quake 
usually is spread over a large area and lasts many seconds. A bomb is 
set off tens of meters underground while true quakes are seated 
kilometers deep. Except for truly minor quakes, like the relaxation 
ones of the City, a quake releases orders more energy than any 
atom bomb. Hence, while some real bomb tests were caught, the bulk of 
the records was a new comprehensive chronicle of earthquakes. 
    The methods and techniques of the Cold War monitoring bases are 
now mainstreamed into modern seismologic stations around the world, 
They give realtime, short leadtime, notice of quakes any where on the 
planet. Data, in addition to being sent to geophysicists, are often 
posted on public websites for anyone to follow. 
P and S waves 
    Quakes raise up two kinds of wave, the same two in mechanical 
systems. The P, pressure, wave moves the material of its medium to and 
fro in line with its own direction of motion. This is similar to a 
sound wave, where the air molecules are squeezed or stretched away 
from the source. The spacing of the squeezed and stretched zones is 
the wavelength. This motion causes the pressure on an obstruction in 
the way, like the ear for hearing. 
    The S, shear, wave moves the medium laterally across its own 
 direction, like a mild water wave. Little pressure is put on an 
obstruction. The water bobs up and down but otherwise stays put. 
    The P and S waves are sometimes called primary and secondary 
because typicly the P waves arrive at a remote place first, followed 
by the S wave. Both do move the ground, so both can inflict damage. 
    The mantle, core, and crust transmit P and S waves differently. By 
mapping the two waves for a quake over the globe, additional 
intelligence about the Earth's interior can be captured. 
    'Tsunami' is a Japanese word. We use it probably because in areas 
of the world affected by tidal waves, Japan was the farthest advanced  
culture to study them first. A tsunami is a mass motion of water 
outward from a quake epicenter that eventually crashes onto land. 
    It rises from a vertical motion of the sea bottom of hundreds of 
meters. Such motion can be a direct upward thrust of the sea floor 
when the colliding plates heave up the crust. Or it could be a drop of 
the floor, collapsing into a chasm between the plates. 
    In either case, a slug of water many kilometers around and 
displaced verticly a hundred meters is then suddenly let go as the 
quake peters out. 
    It is important to understand that tsunamis are NOT a standard 
feature of quakes or volcanos. Most quakes and volcanos agitate the 
ground, causing turbulence in surrounding waters. Cartoons and lousy 
movies make like tsunamis are part of any strong quake. 
    It is only those events that bodily displace the sea floor 
verticly that produce tsunamis. As examples, the June 2005 quake off 
of northern California and the July 2005 undersea volcano near Okinawa 
did not cause tsunamis. 
Force of water 
    Water is not compressible like air. It's volume under force 
remains the same. As the slug of water is let go, it is blocked by 
underlying water and must divert horizontally. There begins a real 
mass migration of water outward from the source. The volume can be 
immense on human scale, hundreds of cubic kilometers. 
    On the high sea away from land and over deep bottom the water can 
spread out and reduce in thickness. The wave may be only a few meters 
high. Ships may not associate such a wave with a tsunami, but treat it 
as a random fluctuation from a distant storm.
    As the wave reaches shallow bottom, approaching land, the volume 
is conserved by piling the mass higher. The wave can reach many tens 
of meters. Unlike a regular wave, the material is actually traveling 
with the wave and is piled up indefinitely far behind it. Thus, the 
land is waved over by a solid block, not a thin wall, of water. 
    Damage is from the mechanical collision of this water against land 
structures. Recall that each cubic meter of water is one ton of mass. 
A chunk of water 5 meters on a side is the equivalent of a train 
engine or military tank! 
    At slow speed, such a collision is messy enough, like that of a 
train and car or tank and fort. The tsunami hits land at hundreds of 
kilometers per hour, way too fast to outrun or elude with no warning. 
Since this mass has a vastly greater kinetic energy transferred to the 
shore obstructions, the damage is all the more violent. Kinetic energy 
for a given mass increases with the square of the speed. 
    Hawaii is a unique case on Earth. It is under the greatest threat 
from tsunamis. Being in the center of the Pacific Ocean, nowhere near 
a plate border, a tsunami anywhere in that ocean can attach Hawaii 
from any direction. 
    Hawaii, from plausible threat and an actual destruction of Hilo in 
the 1940s, built an elaborate early warning and civil defense program 
for future tsunamis. Buoys, satellites, quake stations, airplane 
reports, keep close watch on the ocean movement. The population is 
drilled regularly on responding to alarms and taking certain escape 
roads to the high interior of the islands. 
    Its volcanos, briefly, are not tectonic features. They are built 
from a hole in the underlying crust, perhaps torn out by buckling of 
the Pacific plate, that lets magma ooze to the surface. Hawaii's 
volcanos don't erupt in the conventional volcano sense.  They release 
magma continuously. They are the world's most active volcanos, by its 
myriads of cubic meters of lava sent out every day. 
    Despite their vigor, the Hawaii volcanos are tame enough to visit, 
up to the very craters, under National Park Service supervision. You 
see the lava, steam, noxious fumes close up on paths laid out across 
the volcanos. You also see towns blanketed by lava, some of it still 
too hot to walk on. 
    Hawaii's quakes come from the internal shoving around of magma 
under the volcanos. Because the pressure and stress is continuously 
released, there is little chance for monster quakes like those at the 
Pacific rim. Hawaii, the eternal target of tsunamis will likely never 
generate any of its own. 
    Most people think of the initial water mass approaching the land, 
which is what they see in news films about tsunamis. Tsunamis can come 
in several waves. The original massive block of water may divide into 
several along the way to the target. 
    What happened in past strikes is that rescue teams went to the 
shore after the first wave and were totaled by the second one 
following a couple minutes later. Without remote sensing and realtime 
knowledge of its data, you can not tell on the scene what lies over 
the horizon rushing toward you at jet plane speed. 
    An other cause of afterwaves is diffraction. Water 'bends' around 
obstructions, like islands, much like sound does around furniture in a 
room. You can hear a person while in the 'shadow' of a large cabinet, 
yes, a little weaker than if in the direct line of hearing. Thus, an 
island is vulnerable not only on the side facing the oncoming wave, 
but on all coasts. 
    A third cause is reflection off of distant shorelines, specially 
long ones with cliffs. The tsunami bounces off in an other direction. 
It is a second or higher number wave attacking the target from an 
other direction. When the valley of one wave crosses the peak of an 
other, they net out to yield momentarily a weaker wave. Peak-peak or 
valley-valley intercepts make an amplified wave at that point. The 
result can be a series of waves of assorted, but dangerously large, 
height striking the target over several hours or even a full day. 
Indian Ocean tsunami 
    The tidal wave that striked in the Indian Ocean in December 2004 
emanated from an earthquake in Indonesia. It seems that a large slab 
of ocean floor lapsed into a void between the India and other plate 
during the quake. This set off the immense up-down heave of water that 
radiated away as the tidal wave. 
    This was a singular event for the Indian Ocean, there not being 
any major tsunami before in recorded history. It suffers routine 
quakes, some originating in Indonesia. The nations in this ocean 
regarded tidal waves as a Pacific Ocean factor and never established 
any scheme for detecting, tracking, and then coping with tsunamis. 
    There was no organized warning of any sort. The only effort was by 
haphazard phone calls or emails by geophysicists to colleagues in the 
various target countries. After these colleagues got word, there was 
no way to disseminate alerts to the public and then mount an 
evacuation. The result is now well known from the global news 
    Most people on Earth live along the oceans, simply because the 
water provides transport, drinking, industrial fluid, recreation, 
fishing, and other desirable factors of human existence. The people on 
the ocean are concentrated into towns and cities, some of colossal 
size. New York is not the largest city on Earth, but a very large one 
with about 9-1/2 million residents. This count includes the folk who 
opted out of the census. Around New York is the cosmopolitan zone of 
some 53 million residents. 
    By quirk of geography this region runs parallel to and close by 
the ocean. Virtually all traffic, commerce, business is carried out 
along this zone, with only limited escape routes at right angles to 
it. Hence, for the City, regardless of warning, there is little hope 
of effectively moving its population to safer ground to sit out the 
tidal wave.
    After the tsunami passes, and assuming there was a substantial 
evacuation, there will be little left to return to. Just about every 
structure will be toppled, crushed, soaked, filled with mud and gook. 
Roads and rails will be washed out. Electric, water, and other 
utilities will be cut. Supplies of food, medicine, other necessities 
will be hampered by lack of transport to the target area. 
    For a target like New York, recovery may take decades or even a 
full century because so much of the American civilization will be 
wiped out. The rest of the US, allowing that it was not hit by the 
wave, will be too weak to deliver timely sufficient relief. 
    The situation in almost any other country is far worse. On the 
whole, the US, and parts of Europe, are the highest level of cultural 
advancement on Earth. If it can not, and by all simulations will not, 
survive and sustain a tsunami attack, no one else will. 
    In earlier times, a tsunami striked without warning, instilling 
dread and fear of the ocean. Because a tidal wave can spring from a 
remote, unknown, quake, there was no casual association of the wave 
with a local event, by which in the future to foretell them. 
    Today, we not only have ground bases for watch for the initiating 
quake, but satellite monitoring of ocean movement. If a wave is 
associated with a definite quake, the internal quake waves travel to 
the target within minutes, offering warning if properly interpreted. 
The water wave comes many minutes to hours later, depending on 
distance to the target. 
    Targets may be widely dispersed over the ocean around the quake, 
like they were for the December 2004 event in the Indian Ocean. 
Warnings must be sent to each target in time for defense or escape. 
Such action presumes a developed scheme of alarm and response, plus 
close cooperation among the targets. 
    More locally, buoys are set up in the ocean, as they are along the 
Pacific coast of the US, to watch the water level. Changes indicative 
of a tsunami trigger alarms on shore to initiate defense plans. US 
NOAA in spring 2005 began a project to install such buoys along the 
Atlantic and Gulf coast. These are in anticipation of a plausible 
tsunami rising from the Canary Islands. 
    Only a week earlier I heard the Vesuvius talk, which emphasized 
the futility of moving people from the volcano zone for a predicted 
eruption. Briefly, Vesuvius is surrounding by conurbation, including 
the town of Naples, to within a few kilometers of its crater. Altho 
there were two massive blowups in history, in 79 and 1631, few, if 
any, lessons were learned about living with the volcano. 
    For tsunamis, the only one on the East Coast reliably recorded was 
that associated with the quake in Lisbon, Portugal, in the 1700s. Few 
enough people lived on the coast back then to suffer unrecoverable 
damage. Because no tidal waves happened since then, it was in time 
    The other threat of tsunami comes from the crash of an asteroid. 
The instantaneous conversion of kinetic energy to mechanical motion of 
water could raise global tidal waves that would inundate just about 
all of human civilization. Everywhere, not just in certain countries. 
With the damage so great and remaining resources so little, human 
existence on Earth after an asteroid collision could well be thrown 
back to the stone age level.