Geology

Coastal Communties & Earthquake Tsunami's

For earthquake-generated tsunamis, coastal communities near the epicenter experience casualties and property damage from both the ground shaking of the earthquake and inundation by the tsunami. Powerful tsunami waves interact with coastal processes to change the coastline through erosion and deposition of sediment.

Japanese Tsunami 2011

March 11, 2011 Triggered by M9.0 mega thrust Earthquake Over 16,000 deaths Over $300 billion in damages (most expensive natural disaster ever) 5-8 meters of surface rupture along seafloor Waves of over 33 feet high Struck minutes after the quake

Tsunameter

bottom sensors attached to surface buoys. Detect small changes in the pressure exerted by teh increased volume of water as a tsunami passes overhead. This information is relayed by satellite to a warning center and is combined with tidal gauge information to predict tsunami arrival times

Deep Ocean Tsunami

the tsunami waves move very rapidly and are spaced long distances apart. The spacing between the crests of tsunami waves may be more than 60 miles, and the heights of the waves is generally less than 3 feet. Sailors rarely notice a passing tsunami in the deep ocean.

Tsunami Nearing Land

the water depth decreases, so the velocity of the tsunami also decreases. Near land, the forward speed of a tsunami may be about 28 miles per hour---too fast to outrun, but not nearly as fast as in the open ocean. This decrease in velocity also decreases the spacing between wave crests, that is, the wavelength. As the water slows down and piles up, the height of the waves increases.

Tsunami Warning System

* Network of seismographs to accurately locate and determine the depth and magnitude of submarine and coastal earthquakes * Automated tidal gauges to measure unusual rises and falls of sea level * Network of sensors connected to floating buoys.

Tsunami Characteristics

* Tsunami are long, period, long wavelenth waves * Typical Tsunami: Period - 1 hour, wavelength - 500 miles * Occurs as a series of waves, the fist wave is not always the largest * Trough of wave may appear first causing sea level to drop drastically * Crest of wave follows soon after * Crest of wave can push water inland for several miles

How Do Earthquakes Cause Tsunami's

An earthquake can cause a tsunami by movement of the seafloor and by triggering a landslide. Seafloor movement is probably the more common of these two mechanisms. This movement occurs when the seafloor sits on a block of the Earth's crust that shifts up or down during a quake. In general, it takes an M 7.5 or greater earthquake to create enough displacement of the seafloor to generate a damaging tsunami. The upward or downward movement of the seafloor displaces the entire mass of water, from the sea bottom to the ocean surface.

Extraterrestrial Impact and Tsunami's

Asteroid impact can produce a mega-tsunami, a wave that is about 100 times higher than the largest tsunami produced by an earthquake, and one that could put hundreds of millions of people at risk. Fortunately, the frequency of large asteroid impacts is low.

Indian Ocean Tsunami 2004

Close to 230,000 people were killed, many hundreds of thousands injured, and millions were displaced in more than a dozen countries surrounding the Indian Ocean. With no warning system in place, residents of coastal area after coastal area around the Indian Ocean were struck by a series of tsunami waves without notices. The source of this tsunami was the largest earthquake on Earth in the past 4 decades that struck the morning of December 26, just off the west coast of the Indonesian island of Sumatra. With a magnitude of at least 9.1, this mega thrust earthquake caused the most damaging tsunami in recorded history. More than three-quarters of the deaths were in Indonesia, which experienced both the intense shaking from the earthquake and the inundation by tsunami waves within less than an hour. The giant Indian and Australian plates are being subducted to the northeast beneath the Burma microplate. In this earthquake, the Burma microplate moved about 65 feet to the west-southwest along a gently inclined subduction zone.

Area's Susceptible to Tsunami Risk

Coasts in proximity to major subduction zones or directly across the ocean basin from a major subduction zone (can create M9 or greater EQ's) are at the highest risk. Cascadia Trench along Southwestern South America and subduction zones off coast of Japan

How do Submarine Volcanic Eruptions Cause Tsunami's

Collapse of Volcano flank or explosive submarine eruption

Events that trigger Tsunami's

Earthquakes Landslides Eruptions Extraterrestrial Impact

Run-Up

The movement of a tsunami inland is called the runup of the wave. Runup refers to the furthest horizontal and vertical distance that the largest wave of a tsunami moves inland. The movement of a tsunami inland is called the runup of the wave. Runup refers to the furthest horizontal and vertical distance that the largest wave of a tsunami moves inland.

How Do Landslides Cause Tsunami's

These landslides can take place underwater, where they are referred to as submarine landslides, or they can be large rock avalanches that fall from mountains into the sea. In most cases, the landslides are triggered by an earthquake.

Tsunami Reaching Shore

it may be several meters to several tens of meters high and destroys everything in its path. When the wave arrives, it is more like a very strong and fast-rising increase in sea level. On the rare occasions when tsunamis do break, they may appear as a vertical wall of turbulent water. Once a wave has moved to its farthest extent inland, most of the water then returns back to the open ocean in a strong and often turbulent flow. A tsunami can also generate other types of waves, known as edge waves, that travel back and forth parallel to the shore. The interaction between edge waves and additional incoming tsunami waves can be complex. As a result of this interaction, wave amplification may occur, causing the second or third tsunami wave to be even larger than the first. Most commonly a series of tsunami waves will strike a particular coast over a period of several hours.