5.4.2 Flashcards
Outline how magnitude of earthquakes is measured on Moment Magnitude Scale
The magnitude can be measured on different scales but the one which is reported on the news when an earthquake occurs is the Moment Magnitude Scale (MMS)
It is measured using seismographs
The MMS goes from 1 which are not felt by humans to 10
The MMS is a logarithmic scale which means that a 6 on the scale is a ten times increase in amplitude from a 5
The energy release is 32 times greater
What is earthquake intensity?
The intensity of an earthquake is its impact on people, as well as on the built and natural environments
What scale is used to measure earthquake intensity?
The Modified Mercalli Intensity Scale is used to measure the intensity
The scale goes from I to XII
Outline the general pattern of frequency and regulatory of earthquakes
Low magnitude earthquakes occur much more frequently than high magnitude earthquakes
There are around 20,000 earthquakes around the world every year – that equates to around 55 per day
Most of these are low magnitude and may not even be felt by humans
What is a prediction for occurance of earthquakes?
According to records from 1900, we expect around 16 major earthquakes (magnitude 7.0 or greater) every year
Some years there are more major earthquakes than the long-term average e.g. in 2010, there were 23 major earthquakes
Other years there are less e.g. in 1989, there were only 6
Explain seismic gap theory
Seismic gap theory suggests that if there has been little or no earthquake activity at a plate margin for a long period of time, it is more likely to experience a large earthquake in future
This is because stress will have built up for a longer period of time, so more energy will be released
The theory has been used to identify area at higher risk of large earthquakes
However, it is not precise and not all seismic gaps result in large earthquakes
is it possible to predict earthquake?
It is not possible to predict earthquakes
An understanding of tectonic activity can help scientists identify areas most at risk
95% of earthquakes occur on or near plate boundaries
What is monitored to predict earthquake?
Pre-cursor earthquakes or foreshocks - these are measured using seismometers – they may indicate that a larger earthquake will follow
Deformation - this is measured using strainmeters and tiltmeters - it might indicate that pressure is building up
Groundwater levels - these are measured using sensors – water levels in wells can rise or fall suddenly indicating that an earthquake may be imminent
Radon emissions - these are measured using radon detectors - concentrations of radon gas in the atmosphere can increase prior to an earthquake
Animal behaviour - unusual behaviour can indicate that an earthquake might be about to happen
What is United States Geological Sirvey prediction for earthquakes in Los Angeles?
The United States Geological Survey have made forecasts about the chances of an earthquake in the Los Angeles area:
Within the next 30 years there is a 60% probability of a 6.7 magnitude earthquake
Exam tip
It is important to remember that although significant amounts of time and money has been spent researching the prediction of tectonic hazards, predictions remain unreliable, especially for earthquakes.
