Flashcards in Seismicity- Key Terms Deck (18)
What is seismicity?
The shaking of the earth
What is the focus?
The point within the crust where the pressure release occurs
What is a fault?
A fault is where parts of the crust are being forced to move in opposite directions. Masses of rock get stuck but forces on them continue, building up stresses which create earthquakes
What are seismic waves?
Energy is transferred to surrounding rocks in this form
What is the epicentre?
The place on the Earth's surface immediately above the focus
What is a seismograph?
P and S seismic waves travelling through the interior of the earth are recorded on a seismograph
What are primary waves?
Primary waves are the fastest waves, and move the earth backwards and forwards in a compressional motion. They can move through both solids and liquids
What are secondary waves?
Secondary waves travel at half the speed of P waves and move with a sideways motion , shaking the earth at right angles to the direction of travel. They cannot move through liquids but do much more damage than P waves.
What are surface waves?
Surface waves travel slowest and nearest the ground surface but are the most destructive
What are love waves?
Love waves are surface waves that make the ground move up and down
What are Raleigh waves?
Raleigh waves are surface waves that cause a complex heaving or rolling motion
What is magnitude
Magnitude is the amount of energy released by an earthquake, usually measured on the Richter scale
What is the Richter scale?
The Richter scale is a logarithmic scale with each unit representing a 10 fold increase in strength and a 30 fold increase in energy released
What is the Modified Mercalli Scale
The Modified Mercalli Scale is a scale that measures the intensity of a seismic event and its impact. It is a 12 point scale.
What are aftershocks?
Aftershocks are earthquakes that follow on from the main event and may last for months afterwards. They are generated by the earth settling back after the disruption of the first displacement
What is soil liquefaction?
Soils with a high water content lose their mechanical strength when violently shaken and start to behave like a fluid
What is a tsunami?
A tsunami is giant sea waves generated most commonly by a shallow focus underwater earthquake but also by volcanic eruptions, underwater debris slides and large landslides into the sea.