What is the Elastic Rebound Theory Explains how

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What is the Elastic Rebound Theory? • Explains how energy is stored in rocks

What is the Elastic Rebound Theory? • Explains how energy is stored in rocks – Rocks bend until the strength of the rock is exceeded – Rupture occurs and the rocks quickly rebound to an undeformed shape – Energy is released in waves that radiate outward from the fault

The Focus and Epicenter of an Earthquake • • The point within Earth where

The Focus and Epicenter of an Earthquake • • The point within Earth where faulting begins is the focus, or hypocenter The point directly above the focus on the surface is the epicenter

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt – most of these result from convergent margin activity – ~15% occur in the Mediterranean-Asiatic belt – remaining 5% occur in the interiors of plates and on spreading ridge centers – more than 150, 000 quakes strong enough to be felt are recorded each year

The Economics and Societal Impacts of EQs • • Building collapse Fire Tsunami Ground

The Economics and Societal Impacts of EQs • • Building collapse Fire Tsunami Ground failure Damage in Oakland, CA, 1989

How is an Earthquake’s Epicenter Located? • • • Three seismograph stations are needed

How is an Earthquake’s Epicenter Located? • • • Three seismograph stations are needed to locate the epicenter of an earthquake A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter

Why do earthquakes occur? epicenter • Fractures, faults • Energy released and propagates in

Why do earthquakes occur? epicenter • Fractures, faults • Energy released and propagates in all directions as seismic waves causing earthquakes focus

Crater Lake, Oregon

Crater Lake, Oregon

The Stump of Mount Mazama

The Stump of Mount Mazama

What comes out of a volcano? Ash

What comes out of a volcano? Ash

What comes out of a volcano? Gas Most common: H 2 O CO 2

What comes out of a volcano? Gas Most common: H 2 O CO 2 SO 2 HCl

What comes out of a volcano? Lava

What comes out of a volcano? Lava

Mauna Loa (Hawai’i): A typical shield volcan

Mauna Loa (Hawai’i): A typical shield volcan

Mt. St. Helens: A typical composite volcano

Mt. St. Helens: A typical composite volcano

Mt. St. Helens after its 1980 eruption

Mt. St. Helens after its 1980 eruption

How Calderas Form

How Calderas Form

Plate-tectonic setting of volcanism Explosive (andesitic) volcanoes form at subduction zones.

Plate-tectonic setting of volcanism Explosive (andesitic) volcanoes form at subduction zones.

Plate-tectonic setting of volcanism At spreading centers, low pressure triggers mantle melting—fluid basaltic magma

Plate-tectonic setting of volcanism At spreading centers, low pressure triggers mantle melting—fluid basaltic magma rises.

Plate-tectonic setting of volcanism Within plates, rising plumes of hotter mantle feed hot spots;

Plate-tectonic setting of volcanism Within plates, rising plumes of hotter mantle feed hot spots; varied volcanoes result (basaltic on Hawaii).

Mt. St. Helens Pyroclastic Eruption

Mt. St. Helens Pyroclastic Eruption

Mount Saint Helens- after

Mount Saint Helens- after

Mt. Saint Helens before

Mt. Saint Helens before

Phreatic (vapor) eruption

Phreatic (vapor) eruption

Bulge

Bulge

After the eruption

After the eruption

Pyroclastic eruption

Pyroclastic eruption

Volcanic landscape: A Caldera (Crater Lake)

Volcanic landscape: A Caldera (Crater Lake)