EQ Learning Goals

High magnitude earthquakes are (very/not) frequent

Not

Which range of earthquake magnitude is most frequent?

1-2

Where do a majority of EQs occur at?

Margin of tectonic plates

What is most commonly measured to detect EQ? What is the instrument called?

Ground motion. Seismograph

Where do the largest EQ typically occur?

Edges where continents meet oceans

Describe oceanic plates (movement speed, age, where formed, where destroyed)

Fast moving (cm/yr), young (<200 million years old), formed at mid-ocean ridges, destroyed at subduction zone

Describe continental plates (movement speed, age, subduction behaviour)

Slow moving (mm-cm/yr), much older than oceanic plates. don't get subducted as more buoyant

List 4 types of plate boundary

Divergent, transform, convergent type 1, convergent type 2

Define divergent boundaries (movement (force induced), type of EQ, location where occur)

Plates move apart (tension), smallish EQ occur, happens at mid-ocean ridge

Define transform boundaries (movement (force induced), type of EQ)

Plates move past each other (shear), moderate to large EQ,

Define convergent type 1 boundaries (movement (force induced), plate behaviour, type of EQ)

Plates move toward and collide (compression), less dense plate subducts at subduction zone, largest EQ occur at subduction zone

Define convergent type 2 boundaries (movement (force induced), plate behaviour, type of EQ)

Plates move toward and collide (compression), both plates same density so they crumple, small to very large EQ

Where do the largest EQs occur?

Collision zones

What type of deformation is EQ?

Brittle deformation

Define fault

Region where rocks have broken over time

List 3 types of faults:

Dip slip, strike slip, oblique

Define dip slip fault

Vertical motion along slanting plate

Define reverse fault

Side leaning towards neighbour moves up

Define normal fault

Side leaning on its neighbour drops down

Define strike-slip faults

Motion is horizontal (coming towards you)

Define oblique faults

Motion that's combination of vertical and horizontal motion

Stress is (released/absorbed) by an earthquake, but at the ends of the zone where faults moved, stress can actually (increase/decrease), (raising/decreasing) the likelihood of earthquakes in those areas

released, increase, raise

What is the magnitude of EQ related to?

Energy released when it occurs

List the 3 conditions impacting energy released during EQ

Area of zone broken, strength of rocks broken, amount of motion

List.3 types of ground motion

permanent, slow plastic, short oscillations

List 2 main classes of seismic waves

Body waves, surface waves

Define body waves

Waves that travel through interior of material

Define surface waves (Where travel, how generated, slower/faster than body waves)

Waves that travel only along surface. Generated when p/s-waves arrive at Earth's surface. Slower than body waves

Define p-waves

Particles move back and forth in line with direction of motion

Define s-waves. They (faster/slower) than p-waves?

Particles move side to side, perpendicular to direction wave travelling. Slower

Define rayleigh waves (Motion, damage caused, how it's felt)

Particles experience backward-rotating motion in line with wave's direction. Cause most damage as largest and most clearly felt since travel along Earth's surface

Define Love waves (motion)

Particles experience side-to-side motion perpendicular to wave's direction, horizontal to Earth's surface

What is the main feature required to determine EQ location

Relative times that p and s=waves arrive

Prevention is more/less cost-effective than prediction

more

What evidence suggests Cascadia has potential for large EQ?

Tectonic setting optimal for large subduction zone EQ, large EQ in tree rings, real-time measurements of tectonic deformation, oral history from natives, tsunami record from Japan

What waves cause the most damage?

Rayleigh and love waves

What scale measure felt intensity?

Mercalli scale

What 5 factors influence intensity:

EQ magnitude, duration of shaking, distance to/depth of epicentre/hypocentre, ground type, building characteristics

4 examples of static methods:

Cross brace, shear wall, shear core, isolation

3 examples of active methods

Dampers (absorb energy), adding mass (change resonance), isolation

Define liquefaction

Saturation then shaking of soft materials causing loss of strength

T/F: EQs kill

F