earthquakes Flashcards
(34 cards)
what are earthquakes?
release of stress/ pressure in earth’s crust
where do earthquakes occur?
all plate boundaries (divergent-MID- OCEAN RIDGES-, convergent- OCEAN TRENCHES+ ISLAND ARCS(oceanic-oceanic)-, collision, conservative)
what are the three types of SEISMIC WAVES?
- P waves
- S waves
- surface (L and Rayleigh) waves
what are P WAVES?
- longitudinal waves
- fastest seismic waves
- can travel through liquid and solid (mantle and core)
- arrive first
what are S WAVES?
- transverse waves
- half speed of P waves
- only travels through mantle
what are SURFACE WAVES?
- travel along Earth’s surface/ through the crust
- most destructive waves
- slowest, low frequency
- causes ground shaking
what are the two types of surface waves?
- L WAVES- horizontal shearing of the ground
- RAYLEIGH WAVES- oscillating movement
DEPTH OF FOCUS can influence the impact of an earthquake; what are the two types?
- SHALLOW FOCUS- surface down to 70km
- DEEP FOCUS- 70-700km deep
characteristic of SHALLOW FOCUS
- surface down to 70km
- often occur in BRITTLE ROCKS (resulting from fracturing on rock due to stress in crust)
- more frequent
- LOW LEVELS of ENERGY released but HIGH- ENERGY shallow earthquakes can cause SEVERE IMPACTS
characteristic of a DEEP FOCUS
- 70-700km deep
- INCREASING DEPTHS leads to higher PRESSURE + TEMPS
- less frequent but very powerful
- understanding is evolving
what is the FOCUS
where the earthquake/ shocks originate+ energy is released (below surface)
what is the EPICENTRE?
area on land/ surface impacted directly above focus
what are the three scales assessing earthquake energy?
- Richter scale
- Moment Magnitude scale
- Modified Mercalli scale
what is the RICHTER SCALE?
- uses AMPLITUDE OF SEISMIC WAVES to measure MAGNITUDE
- LOGARITHMIC SCALE from 1-9
- outdates as inaccurate for large earthquakes+ does not calculate how much DAMAGE CAUSED
what is the largest earthquake recorded on Richter scale?
SENDAI earthquake of Pacific coast of HONSHU, JAPAN, 2011
MAGNITUDE 9
what is the MODIFIED MERCALLI SCALE?
- measures earthquake INTENSITY+ IMPACT
- relates ground movement to impacts FELT+ SEEN by those in affected location
- QUALITATIVE ASSESSMENT- based on OBSERVATION+ DESCRIPTION
what is the MOMENT MAGNITUDE SCALE?
- 1-9 scale
- measures energy as related to GEOLOGY
- AREA OF FAULT SURFACE+ AMOUNT OF MOVEMENT ON FAULT
- more accurate than Richter scale, but only for LARGE EARTHQUAKES
MAGNITUDE is only one factor influencing the IMPACT OF A HAZARD; what other factors are there?
- topography
- level of development
- degree of preparation
- shallow/ deep focus (type of hazard)
- communication
(etc.)
what effects can earthquakes have on landforms and landscapes?
MOUNTAIN RANGES created e.g. HIMALAYAS, ASIA
MAJOR FAULT SYSTEMS created e.g. EAST AFRICAN RIFT VALLEY
ENSCARPMENTS created which indicate location of faults
RIFT VALLEYS at DIVERGENT MARGINS formed by downfaulting between parallel faults
how many large earthquakes with the potential to cause destruction and risk to human life each year?
around 100 large earthquakes per year
what HAZARDS are generated by EARTHQUAKES?
- ground shaking+ ground displacement
- liquefaction
- landslides+ avalanches
- tsunamis
- flooding
explain GROUND SHAKING+ GROUND DISPLACEMENT
VERTICAL+ HORIZONTAL movement of ground
SEVERITY DEPENDS ON:
* earthquake magnitude
* distance from epicentre
* local geology
what areas are vulnerable to GROUND SHAKING+ GROUND DISPLACEMENT?
- locations CLOSE TO EPICENTRE with UNCONSOLIDATED SURFACE/ HIGH WATER CONTENT
- BUILDINGS can withstand vertical movement better than horizontal- SWAYING impacts their stability
- displacement of rocks along FAULT LINES can rip apart pipelines, railway tracks, roads, cause infrastructure to collapse etc.
- can disrupt NATURAL DRAINAGE- divert rivers, affect groundwater movement in aquifers (can have severe impacts for PUBLIC WATER SUPPLIES+ IRRIGATION for AGRICULTURE)
explain LIQUEFACTION
VIOLENT GROUNDSHAKING causes SATURATED SOILS (high water content) e.g. sand, silt, alluvium to lose strength+ become fluid; can cause FLOODING (secondary hazard)
