Gg Power Point 11

Front 1

Earthquakes?

Back 1

oscillatory movement of ground from passage of seismic waves through it

Front 2

Faults

Back 2

planes of relative movement. Sudden slippage along faults releases energy transmitted as seismic waves, which pass radially away from the focus of movement.

Front 3

Focus

Back 3

actual origin of the waves

Front 4

Epicenter

Back 4

the point on the Earth’s surface directly above the focus

Front 5

what are two ways of Measuring the “strength” of an earthquake?

Back 5

1. Intensity: Effects from the earthquake
2. Magnitude: Amount of energy released

Front 6

The Modified Mercalli Intensity Scale
mmi

Back 6

Qualitative, somewhat subjective, assessment that measures effects of an earthquake:

- lower values generally deal with the manner in which the earthquake is felt by people.
- upper numbers of the scale are based on observed structural damage

-Intensity decreases with distance away from the EQ epicenter.

1.Not felt except by a very few under especially favorable conditions.
2. Felt by persons at rest, especially on upper floors of buildings.
3. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
4. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
5. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
6. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
7. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
8. Damage slight in specially designed structures; considerable damage in ordinary sugstantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heave furniture overturned.
9. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
10. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
11. if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
12. Damage total. Lines of sight and level are distorted. Objects thrown into the air.

Front 7

The Richter Magnitude Scale

Back 7

Scale of actual energy released during an earthquake

Uses the wave amplitude on a seismogram, corrected for distance from the epicenter.

Open-ended logarithmic scale
4.0 has 100x the wave amplitude as 2.0; actual energy released is 900x

Should get same ML at each station

(Earthquake magnitude does not vary with distance)

Front 8

Moment magnitude (MW) measures:

Back 8

An alternative method (moment magnitude MW) calculates energy release based on the total rupture area of an earthquake

1. Average displacement along fault

2. Area of rupture surface

3. Shear strength of faulted rock

Front 9

Hawai‘i is one of several U.S. regions with high EQ hazard

Back 9

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Front 10

what is the largest “historical” earthquake in the Hawaiian record?

Back 10

-April 2, 1868 – Wood Valley
Estimated magnitude 7.9
77 deaths (31 by landslide; 46 by tsunami)
Earthquake - ground waves up to 0.6 m; houses knocked off foundations, walls and buildings collapsed

-wood Valley Landslide - ~5 km long x 3 km wide and 10 m thick swept down hill at Kapapala, carrying trees, animals and men. 31 men and thousands of animals were killed in the one slide.

-Land subsidence up to 2 meters along the Puna coast

-Tsunami devastated the Ka‘u-Puna coast with wave heights of 12-15 m, destroying buildings and drowning at least 46 people. Wave height ~3 m at Hilo; 2 m at Kealakekua; also observed on Maui and O‘ahu

Front 11

Tsunamis? plus wave speed

Back 11

Tsunamis are a series of elastic waves caused by the propagation of seismic energy through water

Any large-scale displacement of water can generate a tsunami


1. Movement along faults
2. Submarine and near-shore landslides
3. Submarine eruption
4. Meteorite impact

Like earthquakes, most tsunamis are never felt nor detected


-The speed of the waves varies with depth of water.

-Most travel at >800 km/hr (~450 mph) in the deep ocean.

-Waves slow down (but frequency and amplitude increase) in shallower water

For a dangerous tsunami to be generated requires M > 7
Note: tsunamis are not tidal.

-As water depth decreases:
Waves slow down and get closer together
And wave height increases.

-Actual wave height is a complex function of angle of incidence, size and shape of the landmass, bottom slope and other factors

Front 12

Tsunamis are a succession of waves.
There is no relation between the size of a wave and its order
The biggest could be the 1st, 4th or whatever. Later waves can be more severe.

Back 12

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