What is an Earthquake?What is an Earthquake?Earthquakes occur along (within) faults.. It is the abrupt rupture or movement along these structures that triggers

an “earthquake”. These phenomena rarely last even 1 minute yet are responsible for the greatest number of lives

lost (and property damage) due to a natural event!

Where do earthquakes occur? Where do earthquakes occur?

Focus – Focus – point inside the Earth where an point inside the Earth where an earthquake beginsearthquake begins

Epicenter – point on Earth’s surface above Epicenter – point on Earth’s surface above focusfocus

HOW COMMON ARE EARTHQUAKES?

Magnitude (Richter Scale) Number per Year

0 – 3.4 >800,000

4.9 – 5.4 1400

5.5 – 6.1 500

7.0 – 7.3 15

>8 1 every 10 years

MagnitudeMagnitude Magnitude: total size Magnitude: total size

of an effect.of an effect.

Earthquakes are Earthquakes are measured by measured by their magnitude, their magnitude, which is the which is the amount of energy amount of energy released during released during the earthquake.the earthquake.

Intensity ScaleIntensity ScaleThe Roman # that describes the

severity of the earthquake.

Magnitude and IntensityMagnitude and Intensity

Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.

HOW IS THE ENERGY DISPERSED “SPREAD” INTO THE SURROUNDING CRUST?

Types of Seismic WavesThere are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves.

BODY WAVES

P-waves; also known as primary waves or pressure waves

S-waves; also referred to as secondary or shear waves

SURFACE WAVES

Love and Raleigh waves

Typical Typical SeismogramSeismogram

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Primary Waves (P Waves)Primary Waves (P Waves)

A type of seismic wave that A type of seismic wave that compresses and expands the groundcompresses and expands the ground

The first wave to arrive at an The first wave to arrive at an earthquakeearthquake

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Secondary Waves (S Secondary Waves (S Waves)Waves)

A type of seismic wave that moves the A type of seismic wave that moves the ground up and down or side to sideground up and down or side to side

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Body Waves: P & S WavesBody Waves: P & S Waves

Surface Waves: moves along Earth’s surface (most destructive).

How are Earthquakes Measured? How are Earthquakes Measured? Richter ScaleRichter Scale

Richter Equivalent energy yieldMagnitude in TNT Example -1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 1.5 320 pounds 2.0 1 ton Large Quarry or Mine Blast 2.5 4.6 tons 3.0 29 tons 3.5 73 tons 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 5.5 80,000 tons Little Skull Mtn., NV Quake, 1992 6.0 1 million tons Double Spring Flat, NV Quake, 1994 6.5 5 million tons Northridge, CA Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Anchorage, AK Quake, 1964 9.0 32 billion tons Chilean Quake, 1960 10.0 1 trillion tons (San-Andreas type fault circling Earth) 12.0 160 trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy)

SECONDARY EFFECTS SECONDARY EFFECTS ASSOCIATED WITH EARTH QUAKESASSOCIATED WITH EARTH QUAKES

[It is these phenomena that actually kill people, i.e., ground-shaking does not usually harm an individual (maybe their pants!), it is what the shaking does to the surrounding environment that results in bodily harm!]

-Ground shaking (structural collapse, large fissures, etc.)

-Fires (in urban settings; broken gas lines, etc.)

-Landslides

-Ground liquefaction

-Seismic sea waves (Tsunami’s)

Destructive ForceDestructive Force

Earthquakes are classified as Earthquakes are classified as an destructive force due to an destructive force due to the severity of the damage the severity of the damage

that it can cause.that it can cause.

Northridge, CA 1994 (Mag. - 6.7, 10 sec. Northridge, CA 1994 (Mag. - 6.7, 10 sec.

duration)duration)

Northridge, CA 1994 (Mag. - 6.7, 10 sec. Northridge, CA 1994 (Mag. - 6.7, 10 sec. duration)duration)

Loma Prieta, CA 1989 (Mag. – 7.1, 7-15 sec. Loma Prieta, CA 1989 (Mag. – 7.1, 7-15 sec.

durationduration

Kobe, Japan 1995 (Mag. – 7.2)Kobe, Japan 1995 (Mag. – 7.2)

Kobe, Japan 1995 (Mag. – 7.2)Kobe, Japan 1995 (Mag. – 7.2)

Landers, CA 1992 (Mag. - 7.3)Landers, CA 1992 (Mag. - 7.3)

Ground Liquefaction:Ground Liquefaction: Niigata, Japan 1964 (Mag. Niigata, Japan 1964 (Mag. – 7.5)– 7.5)

The Government Hill Elementary school in Anchorage was torn apart by subsidence of the graben at the head of the Government Hill landslide. The south wing of the school dropped about 30 feet (9 m); the east wind split lengthwise and collapsed. The playground became a chaotic mass of blocks and fissures.

Good Friday Quake, Anchorage, AK 1964 (Mag. Good Friday Quake, Anchorage, AK 1964 (Mag.

8.6)8.6)

This slide shows the Turnagain Heights landslide in Anchorage. Seventy-five homes twisted, slumped, or collapsed when liquefaction of subsoils caused parts of the suburban bluff to move as much as 2,000 feet (606 m) downward toward the bay forming a complex system of ridges and depressions.

Loma Prieta, CA 1989 (7.1, 7-15 seconds)Loma Prieta, CA 1989 (7.1, 7-15 seconds)

This slide shows a fire at Valdez, Alaska, The tank fire was triggered by failure of oil storage tanks at the Union Oil tank farm. By 10:30 p.m. about 5 hours after the quake, the whole waterfront was burning furiously. Some buildings along Front Street and Standard Oil's pumping control station also caught fire. The Union Oil tank farm continued to burn for two weeks.

This view, taken a few months after the earthquake, is looking north along the waterfront at Seward. Note the "scalloped' shoreline left by the underwater landslides, the severed tracks in the railroad yard which dangle over the landslide scarp, and the heaps of railroad cars and other debris thrown up by the tsunami waves. This massive submarine landslide destroyed a large portion of the Seward waterfront during the quake.

Living spruce trees up to 24 inches in diameter and between 88 and 101 feet above sea level were broken and splintered near Shoup Bay by the surge-wave generated by an underwater landslide in Port Valdez, Prince William Sound.

Tsunami Generated by Earthquake of March 27, 1964, Prince William Sound, Alaska. Surge wave left 2 x 12 in. plank in truck tire at Whittier, Alaska. One of the waves, probably the same one that caused the major damage in Whittier, reached a height of 31.7 m above low tide.At Whittier the waves destroyed two saw mills; the Union Oil Company tank farm, wharf and buildings; the Alaska Railroad depot; numerous frame dwellings; and the railroad ramp handling towers at the army pier. They also caused great damage to the small boat harbor. The tsunami killed thirteen people at Whittier, a community of 70 people.

Aftermath of the Chilean tsunami in the Waiakea area of Hilo, Hawaii, 10,000 km from the generating area. Parking meters were bent by the force of the debris-filled waves. Note the scattered debris and the gutted foundation. The earthquake off the coast of central Chile generated this tsunami that affected the entire Pacific Basin. One of the most seriously affected areas was Hilo, Hawaii, where 61 deaths and $23 million in damage occurred.

What Controls the Level of Shaking?

Magnitude The more energy released, the greater potential for damage, regardless of all other factors (and greater areal extent).

Distance Shaking decays with distance

Local soils and bedrock geologySoil characteristics may amplify the shaking.

(seasonal climatic variations can impact this)

Complex geology tends to dampen waves

FACTORS EFFECTING THE DESTRUCTIVENESS OF AN EARTHQUAKE

Building codes and materials

Date Location Deaths MagnitudeJan. 23, 1556 Shansi, China 830,000 n.a.July 27, 1976 Tangshan China 655,000 8Aug. 9, 1138 Aleppo, Syria 230,000 n.a.May 22, 1927 near Xining, China 200,000 8.3Dec. 22, 856 A.D. Damghan, Iran 200,000 n.a.Dec. 16, 1920 Gansu, China 200,000 8.6Mar. 23, 1932 Ardabil, Iran 150,000 n.a.Sept. 1, 1923 Kwanto, Japan 143,000 8.3Oct. 5, 1948 Ashgabat, USSR 110,000 7.3Dec. 28, 1908 Messina, Italy 70-100,000 7.5Sept. 1290 Chihli, China 100,000 n.a.Nov. 1667 Shemakha, Caucasia  80,000 n.a.Nov. 18, 1727 Tabriz, Iran  77,000 n.a.Nov. 1, 1755 Lisbon, Portugal  70,000 8.7Dec. 25, 1932 Gansu, China  70,000 7.6May 31, 1970 Peru  66,000 7.8 1268 A.D. Silicia, Asia Minor  60,000 n.a.Jan. 11, 1693 Sicily, Italy  60,000 n.a.May 30, 1935 Quetta, Pakistan  30-60,000 7.5Feb. 4, 1783 Calabria, Italy  50,000 n.a.June 20, 1990 Iran  50,000 7.7

The deadliest earthquakes on record (in terms of lives

lost).