Earthquakes Flashcards
who is a person who studies movement in the Earth’s crust
a seismologist
what is the oldest instrument used to measure the magnitude of a quake
a seismograph
how does a seismograph function
a rotating drum has graph paper attached to it. when vibrations occur, the arm vibrates and at same time draws lines on graph paper. the paper can later be removed to display an image that gives details about the magnitude and duration of the quake
describe the different wavelengths on the seismograph
the greater the wavelength drawn by the seismograph, the stronger the earthquake. straight lines indicate periods of no vibrations
do we still use the same seismographs today
no, they are know more sophisticated and some are fully computerised
what did we used to use to measure intensity of earthquakes, what do we use now and what do these 2 things have in common
originally the Richter was used but more recently the Movement Magnitude Scale has been used. these 2 scale both have a maximum rating of 10.
how many earthquakes occur at plate edges
90%
what is the estimated time of an earthquake occuring
an earthquake every 10 seconds, but most can’t be felt
how are seismic waves formed and what are they
when plates slip and grind against each other forming vibrations below ground which send shock waves in concentric circles away from the focal point. these waves are referred to as seismic waves
what is the focal point
the point where vibrations first occur
what is the epicentre
the point on the surface above the focal point is referred to as the epicentre of an earthquake. this is where the earthquake is its strongest.
why do aftershocks occur
aftershocks occur because the Earth’s crust has to settle. these aftershocks have a lower magnitude than the main earthquake.
what is a fault plane
cracks in Earth’s crust where earthquakes occur
what are the 3 different types of fault planes and describe them
1 - a normal fault
because of tension, a crack in Earth’s crust forms. as 2 sections of crust are pulled apart, 1 slides down in relation to the other, grinding against each other.
E.g - Christchurch Fault, South Island, New Zealand
2 - a reverse fault
converging pressure at fault plane forces 1 section of Earth’s crust to thrust upwards in relation to other. as it is forced upwards, 2 sections of crust grind against each other.
E.g - Himalaya Mountains in Tibet
3 - a transverse fault
transverse forces cause 2 sections of Earth’s crust to slide against each other at some time grinding against each other to form vibrations.
E.g - St Andreas Fault, along Californian Coast
learn 2 different earthquakes
do you now them well
