Comprehensive Earthquake Science: Faults, Waves, Scales, and Mitigation

Earthquake

Sudden release of energy due to movement along a fault

Fault

Fracture between two blocks of rock

What causes earthquakes?

Stress builds exceeds friction sudden movement releases energy

Where do most earthquakes occur?

Near plate boundaries

Hypocenter (focus)

Location underground where the earthquake starts

Epicenter

Point on Earth's surface directly above the hypocenter

Seismometer

Instrument that measures ground shaking

Seismogram

Record graph of seismic waves

P waves (Primary waves)

Fastest waves arrive first

S waves (Secondary waves)

Slower waves arrive after P waves

Which waves arrive first?

P waves

What is the P-S wave time difference used for?

To determine distance from the earthquake

How do you locate an epicenter?

Use 3 or more seismometers and triangulation circle intersections

Mercalli Scale

Measures intensity how strong shaking feels qualitative

Richter Scale

Measures magnitude using seismograms logarithmic older scale

Richter scale increase of 1 means

10 times more shaking

Moment Magnitude Scale (Mw)

Modern scale measuring total energy released

Mw scale increase of 1 means

About 32 times more energy

Which scale is used today?

Moment Magnitude Scale Mw

Normal Fault

Hanging wall moves down caused by extension

Reverse (Thrust) Fault

Hanging wall moves up caused by compression

Strike-Slip Fault

Blocks move horizontally past each other

Extension stress

Pulling apart

Compression stress

Pushing together

Shear stress

Sliding past each other

Main earthquake hazard

Ground shaking

Liquefaction

Ground behaves like a liquid during shaking

Tsunami

Large ocean wave caused by underwater earthquakes

How are tsunamis different from normal waves?

Travel faster and grow taller near shore

Factors that affect earthquake damage

Population distance to cities depth building quality time of day

Why can two earthquakes of same magnitude have different impacts?

Different locations population and infrastructure

Seismogram X-axis

Time

Seismogram Y-axis

Amplitude strength of shaking

First waves on a seismogram

P waves

Second waves on a seismogram

S waves

Largest waves on a seismogram

Surface waves

If P-S gap is large what does it mean

Far from epicenter

If P-S gap is small what does it mean

Close to epicenter

What is the primary aim of this week's lesson?

To predict where a big earthquake will occur based on real data.

What short-term measures can mitigate casualties during large earthquakes?

Earthquake education and early warning systems.

What is the impact of oscillation frequency on buildings during an earthquake?

It determines which buildings collapse based on their natural oscillation frequency.

What engineering tools can be used to mitigate earthquake damage?

Base isolation, vibration control dampers, and pendulum damping.

What was the magnitude of the earthquake that killed almost 9,000 people in April?

Magnitude 7.8.

What type of buildings collapsed during the 1985 Mexico City earthquake?

Mid-rise (~10 storey) buildings.

Why did mid-rise buildings collapse during the Mexico City earthquake?

The frequency of the earthquake wave matched the natural oscillation frequency of the buildings.

What happens to frequency when the period of an earthquake wave increases?

Frequency decreases.

In which material is earthquake frequency higher: hard bedrock or soft sediment?

Hard bedrock.

What type of building is most likely to collapse at low frequencies (<1 s period)?

Mid-rise buildings.

What is a short-term preparedness measure mentioned for earthquakes?

Early warning systems like USGS ShakeAlert.

What is a long-term preparedness measure for earthquakes?

Hazard mapping.

What does hazard mapping help identify?

Areas at risk for seismic activity.

What are the ancient faults represented in geologic maps?

Solid black lines indicating past seismic activity.

What is base isolation in earthquake engineering?

A technique that allows a building to move independently of ground motion.

What are vibration control dampers used for?

To reduce the amplitude of vibrations in buildings during an earthquake.

What is pendulum damping?

A method using a pendulum to absorb seismic energy.

What is the relationship between earthquake wave period and frequency?

They are inversely correlated; as period increases, frequency decreases.

What should be considered when predicting the location of a big earthquake?

Data from previous earthquakes and geological features.

What are warning signs of a potential volcanic eruption?

Small earthquakes, small eruptions, and ground deformation.

What is the significance of the USGS in earthquake preparedness?

They provide data and early warning systems for seismic activity.

What type of earthquake education is emphasized for higher risk regions?

Community awareness and preparedness training.

What does the term 'oscillation frequency' refer to in the context of earthquakes?

The rate at which ground motion occurs during an earthquake.

What is the role of geologic maps in understanding earthquake risks?

They show fault lines and historical seismic activity.

What is the expected outcome of hazard mapping?

Improved understanding of earthquake risks and better preparedness.

What is the relationship between building height and earthquake wave frequency?

Higher buildings may resonate differently with varying earthquake frequencies.

What is a critical factor in determining building stability during an earthquake?

The building's natural oscillation frequency relative to the earthquake wave frequency.

What are the three main scales used to measure earthquake magnitude?

Mercalli scale, Richter scale, Moment magnitude scale

What does the Mercalli scale measure?

The amount of shaking felt in a specific location

What is the primary limitation of the Mercalli scale?

It does not capture the quantitative magnitude of an earthquake

Who developed the Richter scale?

Charles Richter and Beno Gutenberg in the 1930s

What is a key characteristic of the Richter scale?

It is a logarithmic scale that measures earthquake magnitude based on seismogram amplitude

What is the Moment magnitude scale (MW)?

A scale that quantifies the amount of energy released during an earthquake and is globally applicable

How much more energy is required to produce a magnitude 7 earthquake compared to a magnitude 6 earthquake?

32 times more energy

What is the significance of the logarithmic scale in earthquake measurement?

It indicates that each whole number increase on the scale represents a tenfold increase in measured amplitude and approximately 31.6 times more energy release

What are the types of faults associated with earthquakes?

Normal, reverse, and strike-slip faults

What is liquefaction in the context of earthquakes?

A phenomenon where saturated soil loses strength and stiffness during shaking, causing it to behave like a liquid

What are some hazards associated with earthquakes beyond shaking?

Tsunamis, liquefaction, landslides, and avalanches

What does the Moment magnitude scale incorporate in its calculations?

The strength of the ruptured crust, rupture area, and fault slip distance

What is the purpose of ShakeMaps?

To show the distribution of shaking intensity based on qualitative assessments from multiple locations

What is the difference between regular waves and tsunamis?

Tsunamis are long-wavelength waves caused by underwater disturbances, while regular waves are generated by wind

What was the original purpose of the Mercalli Intensity scale?

To describe the intensity of shaking experienced by people and structures

What geographic factors can affect earthquake risks?

Local geology, population density, and infrastructure resilience

What is the significance of the 2011 Great Tohoku Earthquake?

It was a major earthquake that caused widespread devastation and tsunamis in Japan

How does a magnitude 7 earthquake's shaking compare to a magnitude 4 earthquake on the logarithmic scale?

A magnitude 7 earthquake has 1000 times more shaking than a magnitude 4 earthquake

What is the role of seismological institutions like the USGS?

To monitor and report on seismic activity and earthquake hazards

What are the learning outcomes for this week's lesson on earthquake hazards?

Compare magnitude scales, assess risks, explain wave differences, observe tsunami effects, and identify fault types

What is the purpose of assessing earthquake hazards?

To understand risks and prepare for potential impacts on communities and infrastructure

What is a tsunami?

A series of ocean waves caused by large underwater disturbances, such as earthquakes

What does the term 'seismic moment' refer to?

A measure of the total energy released during an earthquake

What is a key feature of the Moment magnitude scale compared to the Richter scale?

It is applicable worldwide and provides a more accurate measure of larger earthquakes

What is the main takeaway regarding the Richter scale's applicability?

It is effective for low to moderate magnitudes but not for high magnitudes or in regions outside California

What are the three main earthquake hazards beyond shaking?

Liquefaction, landslides, and avalanches.

What is liquefaction?

A phenomenon where saturated soil substantially loses strength and stiffness in response to applied stress, often during an earthquake.

What geographic factors can influence earthquake hazards?

Location, population density, and proximity to major population centers.

What is the significance of earthquake magnitude?

Magnitude indicates the energy released during an earthquake, but other factors like depth and location also affect its impact.

Compare the 2010 Haiti earthquake and the 2010 New Zealand earthquake in terms of magnitude.

Haiti had a magnitude of 7.0, while New Zealand had a magnitude of 7.1.

What were the death tolls for the Haiti and New Zealand earthquakes in 2010?

Haiti had approximately 160,000 deaths; New Zealand had 2 deaths.

What was the depth of the hypocenter for the Haiti earthquake?

6 miles.

What was the depth of the hypocenter for the New Zealand earthquake?

8 miles.

How does population density affect earthquake impacts?

Higher population density can lead to more casualties and damage during an earthquake.