Instrument which measures and detects seismic waves/vibrations

Weight and pen remain still during an earthquake; drum moves with the Earth

Earthquake measuring stations have at least 3 seismographs

Locations of epicenters are determined using data from 3 measuring stations

Photo courtesy of : http://www.thetech.org/exhibits/online/quakes/seismo/

Written record of earthquake wavesUsed to determine epicenter and

when earthquakes occurredShows magnitude (strength) of waves

with height of lines

Epicenter: surface origin of seismic waves (surface waves) directly above focus

Focus: underground point of origin for earthquake body waves

*Primary or Pressure waves

*fastest

*travel through solid, liquid, gas

*alter speed due to density;the denser the material, the faster they move

*push-pull waves

*rock moves back and forth in the direction of the wave

*Secondary waves

*travel through solids only

*the denser the material, the faster these move

*rocks move side to side at right angles to the direction of

the wave

*L waves

*slowest moving; originate at epicenter

*cause the most serious damage

*travel along the surface of the Earth

*move crust up and down & back and forth

Why do you need

3

stations reporting the

same earthquake data?

Triangulation results in one epicenter location.

What information do

you need from the 3

reporting stations and

why do you need it?

The difference in arrival times of the P and S waves (lag time)

and then the distance to the epicenter

The lag time determines the epicenter.

Which of the stations is farthest from the epicenter?

Which of the stations is closest?

How do you know?

1

2

3

S-P Time Method:Collect data from at least 3 seismograms from an earthquakeUse the Time-Distance graph to find distance from epicenter for each seismogramUse each distance to draw a circle of possible epicentersThe actual earthquake epicenter is found at the spot where all 3 intersect

•Strength of earthquake waves•Measured by Richter Scale

•Scale from 0-10•Each increasing number is 10x more

ground shaking

•A measure of how much damage is done and

the degree to which an earthquake is felt

by people•Measured by Modified Mercalli Scale

•Scale from I-XII•Each location that felt the event will have a different intensity level

A magnitude 8.7 earthquake is 794 times BIGGER on a seismogram than a magnitude 5.8 earthquake. The magnitude scale is logarithmic, so

(10**8.7)/(10**5.8) = (5.01*10**9)/(6.31*10**6) = .794*10**3 = 794 OR = 10**(8.7-5.8) = 10**2.9 = 794.328 Another way to get about the same answer without using a calculator is that since 1 unit of magnitude is 10 times the amplitude on a seismogram and 0.1 unit of magnitude is about 1.3 times the amplitude, we can get,

10 * 10 * 10 / 1.3 = 769 times [not exact, but a decent approximation]

The magnitude scale is really comparing amplitudes of waves on a seismogram, not the STRENGTH (energy) of the quakes. So, a magnitude 8.7 is 794 times bigger than a 5.8 quake as measured on seismograms, but the 8.7 quake is about 23,000 times STRONGER than the 5.8! Since it is really the energy or strength that knocks down buildings, this is really the more important comparison. This means that it would take about 23,000 quakes of magnitude 5.8 to equal the energy released by one magnitude 8.7 event. Here's how we get that number:

One whole unit of magnitude represents approximately 32 times (actually 10**1.5 times) the energy, based on a long-standing empirical formula that says log(E) is proportional to 1.5M, where E is energy and M is magnitude. This means that a change of 0.1 in magnitude is about 1.4 times the energy release. Therefore, using the shortcut shown eartlier for the amplitude calculation, the energy is,

32 * 32 * 32 / 1.4 = 23,405 or about 23,000

The actual formula would be:

((10**1.5)**8.7)/((10**1.5)**5.8) = 10**(1.5*(8.7-5.8)) = 10**(1.5*2.9) = 22,387 This explains why big quakes are so much more devastating than small ones. The amplitude ("size") differences are big enough, but the energy ("strength") differences are huge. The amplitude numbers are neater and a little easier to explain, which is why those are used more often in publications. But it's the energy that does the damage.

Liquefaction

Vibrations cause pressure in ground water between grains of sand and silt. This turns sand into a viscous liquid ”quicksand”.

Tsunamis

giant waves that travel at speeds of 700-800 km/hr

and reach height of 20+meters

Earthquake hazard is a measurement of how likely an area is to have damaging quakes in the future.

It’s deter-mined by past and present seismic activity

Seismologists look for patterns in earthquake data to try and predict future earthquakes.

The strength and frequency are important factors in the prediction of earthquakes.

Some seismologists believe that a major earthquake is more likely to occur along part of an active fault that have had few

or no earthquakes happen in recent times. This is known as the…

Used to predict the Quake of ’89 (Loma Prieta)

The area along an active fault where few earthquakes have happened is called a seismic gap.

The location and magnitude of this quake was predicted by using the gap hypothesis.

Changes in speed of P and S waves

Other observations that may be helpful when predicting ‘quakes include:

Changes in the tilt of the Earth’s surface

Changes in the behavior of animals

These methods are not completely accurate and will only suggest

that an earthquake may occur

Changes in water level (lakes, streams, wells, etc.)

Space-based technology helps geologists identify movement patterns that precede major earthquakes.

Mass damper- helps compensate for building movement

Active tendon system- helps compensate for building movement

Base isolators- shock absorbers that stop the passing of seismic waves

Cross braces-counteracts the pull and push stresses

Flexible pipes- prevent water and gas lines from rupturing

Some things that help:

A lead-rubber bearing is made from layers of rubbers sandwiched together with layers of steel. In the middle of the bearing is a solid lead "plug." On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. (See Figure 2) The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.

Before: Survival supplies

Identify safe zones inside and outside

Evacuation plan and plan where to meet

During: Inside-Seek cover under table, desk,

Outside- Face down away from buildings, trees, powerlines

After: Stay out of damaged buildings, be prepared for aftershocks