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?

Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus

HOW COMMON ARE EARTHQUAKES? Magnitude (Richter Scale)Number per Year 0 – 3.4 >800, – – – >81 every 10 years

Magnitude  Magnitude: total size of an effect.  Earthquakes are measured by their magnitude, which is the amount of energy released during the earthquake.

Intensity Scale The Roman # that describes the severity of the earthquake.

Magnitude 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 Waves There 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 Seismogram

Primary Waves (P Waves)  A type of seismic wave that compresses and expands the ground  The first wave to arrive at an earthquake

Secondary Waves (S Waves)  A type of seismic wave that moves the ground up and down or side to side

Body Waves: P & S Waves

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

How are Earthquakes Measured? Richter Scale

Richter Equivalent energy yield Magnitude in TNTExample ounces Breaking a rock on a lab table pounds Large Blast at a Construction Site pounds ton Large Quarry or Mine Blast tons tons tons 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) ,000 tons ,000 tons Little Skull Mtn., NV Quake, million tons Double Spring Flat, NV Quake, million tons Northridge, CA Quake, million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon million tons Landers, CA Quake, billion tons San Francisco, CA Quake, billion tons Anchorage, AK Quake, billion tons Chilean Quake, trillion tons (San-Andreas type fault circling Earth) trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy)

SECONDARY EFFECTS ASSOCIATED 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 Force Earthquakes are classified as an destructive force due to the severity of the damage that it can cause.

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

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

Kobe, Japan 1995 (Mag. – 7.2)

Landers, CA 1992 (Mag )

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

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 geology Soil 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

The deadliest earthquakes on record (in terms of lives lost).