Earth and Earthquake

• This brittle outermost layer varies in thickness from about 25 to 70 km under continents, and from about 5 to 10 km under the oceans

  The Crust
• It consists of dense silicate rocks. Both P- and S-waves from earthquakes travel through it

  The Mantle
• At a depth of about 2900 km is the boundary between the mantle and the Earth's core. It is composed of iron and we know that it exists because it refracts seismic waves creating a 'shadow zone'

  The Core
• the process that changes solid rock into sediments


  Weathering
• the process that moves the sediments away from its original position

  erosion
• four forces of erosion

  water, wind, glaciers, and gravity
• responsible for most erosion

  Water
• While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering and mass wasting gradually wear those rocks and landscapes away.

  Denudation
• weathering that breaks rock into smaller pieces

  Mechanical weathering
• main form of mechanical weathering in any climate that regularly cycles above and below the freezing point

  Ice wedging/freeze-thaw weathering
• another form of mechanical weathering. One rock bumps against another rock.

  Abrasion
• Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside

  talus
• Is the shaking or trembling caused by the sudden release of energy, usually associated with faulting or breaking rocks.

  Earthquakes
• Is the study of earthquakes and the waves they create.

  Seismology
• Is a scientist who study and measure earthquakes to learn more about them and to use them for geological discovery.

  Seismologist
• Are the recordings of the ground shaking at the specific location of the seismograph

  Seismograms
• Are recording instruments used to record the motion of the ground during an earthquake.

  Seismographs
• It is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with seismograph.

  Seismometer
• Is the place of origin of the earthquake in the interior of the earth

  Focus, Origin, Center, Hypocenter
• Is the place on the earth’s surface, which lies directly above the center of the earthquake.

  Epicenter
• Is the point on the earth’s surface diametrically opposite to the epicenter.

  Anticenter
• Is the imaginary line which joins the center and the epicenter. This represents the minimum distance which the earthquake has to travel to reach the surface of the earth.

  Seismic Vertical
• Is an imaginary line joining the points of same intensity of the earthquake.

  Isoseismal
• Is an imaginary line which joins the points at which the earthquake waves have arrived at the earth’s surface at the same time.

  Coseismal
• Is the form of the transmitted energy released from the focus at the time of the earthquake.

  Seismic Waves
• Is proportional to the energy released by an earthquake at the focus. It is calculated from earthquakes recorded by a seismograph. It is represented by Arabic Numbers (e.g., 4.8, 9.0).

  Magnitude
• Is the strength of an earthquake as perceived and felt by people in a certain locality. It is a numerical rating based on the relative effects to people, objects, environment and structures in the surrounding area. The intensity is generally higher near the epicenter. It is represented by Roman Numerals (e.g., II, IV, IX).

  Intensity
• In the Philippines the intensity of an earthquake is determined using what?

  PHIVOLCS Earthquake Intensity Scale (PEIS)
• Classifications of Earthquakes

  Based on the depth of the focus and the cause of occurrence
• Earthquakes with a focus depth of less than 50 km

  Shallow Earthquakes
• Earthquakes with a focus depth of more than 50 km but less than 250 km

  Intermediate Earthquakes
• Earthquakes with a focus depth of more than 250 km

  Deep Earthquakes
• Exclusively due to internal causes, i.e., due to disturbances or adjustments of geological formations taking place in the earth’s interior.

  Tectonic Earthquakes
• are generally due to external or surfacial causes. Like sudden and major landslides, volcanic eruptions, man-made explosions and collapse of caves, tunnels, etc.

  Non-Tectonic Earthquakes
• Types of Faults

  Normal, Reverse, Strike-slip
• large solid pieces of lithosphere, ranging in thickness from 5–10 km in deep oceans to over 70 km beneath large mountain ranges, which together form the Earth’s crust.

  Tectonic Plates
• Plates can move apart at a boundary. This type of boundary is called a divergent boundary. It is also referred to as a constructive plate boundary, as new material is being produced at the boundary surface

  Divergent Boundaries
• Continental collisions result in the creation of mountains and fold belts as the rocks are forced upwards. Plates can move towards each other at a boundary.

  Convergent Boundaries
• the boundary is between an oceanic plate and a continental plate,

  destructive plate boundary
• produce the deepest earthquakes

  subduction zones