EARTHQUAKES AND FAULTS

Ring of Fire: trenches and associated subduction zones that surround the Pacific Ocean

What is an earthquake?

Causes of EarthquakesTectonic stress (most common)Water added under pressureGeothermal gradientRock typeFast/cold versus slow/warm rate and temperature

Causes of EarthquakesStress accumulation and energy release at plate boundaries.

Explain the 3 different types of stresses Tensionpulls apart

What is a fault?A fault is a break in the rocks that make up the Earths crust, along which rocks on either side have moved past each other.

The direction of movement along the fault plane determines the fault type.

Explain the 3 different types of stressesPushes togetherCompression

Explain the 3 different types of stresses Tensionpulls apart

Explain the 3 different types of stressesShearing Rocks move in two opposite directions

Three Kinds of faults major FaultsStrike-slipReverseNormal

Normal FaultThe hanging wall moves down relative to the foot wall.

This fault type is caused by tensional stress.

Normal Fault

Normal Fault

Normal Fault

Reverse FaultThe hanging wall moves up relative tothe foot wall.

This fault is caused by Compressional stress.

Reverse Fault

Reverse Fault

Reverse Fault

Strike-Slip FaultThe fault exists between two pieces of crust and the Movement occurs horizontally where the sides slide past each other.This fault type is caused by shear stress.

Strike-Slip Fault

Strike Slip Fault

Strike-Slip Fault

Fault Movement = EarthquakesAn earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

Faults in the PhilippinesPhilippine Fault Zone- longest fault system in the Philippines. From ilocos norte, Abra, La union, Quezon, Masbate, Leyte, Agusan, Compostela Compostela Valley and Davao Oriental

In Luzon- Dumon River Fault System in Cagayan and West Ilocos, Iba, Zambales, Marikina, Rodriguez and San Mateo, Rizal, Pasig, Taguig, Muntinlupa, San Pedro, Binan, Calamba, Santa Rosa, Carmona, Tagaytay, Cavite , Mindoro

In Visayas- Negros and BoholIn Mindanao- Lanao fault System, Davao, Central Mindanao and Tangbulan.

Focus- where the slip happens below ground

Epicenter-where the shaking is first felt above ground directly above the focus.

FOCUSPoint in Earths interior where seismic waves originated. Focus can be 5 to 700 km below the surface of the earth. Seismic waves travel outward in all direction from the focusThe primary and secondary waves originates from an earthquakes focus.

EPICENTERThe point on the earth surface directly above the focus.

Primary WavesP waves- are the first waves to arrive at a seismograph station. -fastest form of wave, sometimes called compression waves.Can move through both liquids and solids. These waves cause rock particles to move back and forth in the same direction as the wave is traveling (push-pull).

S-Waves- arrive after the primary waves at the seismograph station. -Can travel through solids only. -Cause particles to move back and forth at right angles to the line of wave movementSecondary Waves

SEISMOLGY EARTHQUAKE LOCATION Travel time versus distance plotsCan construct distance versus travel time for earthquakes knowing properties of earths interior

Note that with increasing distance the arrival times for the various waves separates.

The 3 min 45 sec difference between the arrival time of the P and S waves corresponds to a distance of 2000 km.

SEISMOLOGYLOCATING EARTHQUAKESTriangulation-Need three different seismic stations to locate an earthquake.-Measure the P-S arrival times and convert these to distance.-Triangulate using radius given by P-S travel times.-Triangulation for position of an earthquake near New Madrid using stations in Columbus, St Louis and Memphis

Surface WavesRayleigh wave-surface wave causing the ground to shake in an elliptical motionBecause of its motion, it moves the ground up and down, and side-to-side in the same direction that the wave is movingMost of EQ shaking is due to this type of wave

Measuring EarthquakesMagnitude- the amount of energy released during an EQIntensity- measures the amount of effectRichter Magnitude Scale- based on the largest seismic waves generated by the EQ on a factor of 10.Moment Magnitude Scale- considers the size of the fault rupture, the amount of movement, and rocks stiffness

Modified Mercalli ScaleMeasures the intensity of the EQ using a rating system of the damageScientists compile information from various observers within different zip codes to get a better understanding of the devastation caused by an EQ to determine its intensity.

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