# 6th Grade Science - Earthquakes

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Holt Science and Technology - Eatch Science. c 2005. Chapter 8

### seismology

the study of earthquakes

### deformation

the bending, titling and breaking of the Earth's crust; the change in the shape of rock in response to stress

### elastic rebound

the sudden return of elastically deformed rock to its undeformed shape

### Plate Motion: Transfrom

Fault Type: Strike-slip

### Plate Motion: Convergent

Fault Type: Reverse

### Plate Motion: Divergent

Fault Type: Normal

### seismic wave

a wave of energy that travels throught the Earth, away from an earthquake in all directions

### P wave

a seismic wave that causes particles of rock to move in a back-and-forth direction, the fastest seismic wave

### S wave

a seismic wave that causes particles of rock to move in a side-to-side direction, the secondary seismic wave

### seismologists

are scientists who study earthquakes and sesmic waves

### fault

a break in the Earth's crust along which blocks of the crust slide relative to one another; due to tectonic forces

### plastic deformation

deformation that is like clay, moveable, does not cause earthquakes

### elastic deformation

when the rock can only be stretched to a certain point before breaking(does lead to e quakes)

### San Andreas Fault

An earthquake zone in California where the Pacific Plate and the North American Plate slide past each other, frequently causing earthquakes

### earthquake zone

area where earthquakes are common; where a large number of faults are located

### body waves

seismic waves that travel through the Earth's interior

### surface waves

seismic waves that travel along the Earth's surface

### seismograph

an instrument that records vibrations in the ground and determines the location and strength of an earthquake

### seismogram

a tracing of earthquake motion created by a siesmograph

### epicenter

point on Earth's surface directly above an earthquakes starting point, or focus

### focus

the point along a fault at which the first motion of an earthquake occurs

### Ricther scale

measures the magnitude or strength of an earthquake

### earthquake hazard

This measures how likley an area is to have damaging earthquakes in the future, it is determined by past and present seismic activity

### gap hypothesis

a hypothesis that states that a major earthquake is more likely to occur along the part of an active faults that have had relativley few earthquakes in a certain period of time

### seismic gap

area along a fault where few earthquake have happened recently but where strong earthquakes have happened before

### retrofitting

the process of making older structures more earthquake resistant

### mass damper

What is a weight placed in the roof that is computer sensored to move and counteract an earthquake

### active tendon system

a weight in the building's base, similar to the mass damper

### base isolators

act as shock absorbers during an earthquake, makde of layers of rubber or steel wrapped around a lead core; absorb seismic waves to avert their travel through the building

### cross braces

steel braces in between the floors that support the building during earthquakes

### flexible pipes

help prevent water and gas lines from breaking during an earthquake

### West Coast

part of the contenental US that has the highest earthquake-hazard level

### how is the strength of earthquakes related to how often they occur

the higher the magnitude of the earthquake, the less frequently they occur

### aftershock

an earthquake that occurs after a larger earthquake in the same area

### newest technology

is what architects and engineers use to design and build structures to withstand earthquakes

### common way to retrofit an older home for earthquakes

is to securely fasten it to its foundation

### what can you do to make your home safer before an earthquake

put heavier things on lower shelves and prepare food, water and first aid kits

### what are some plans you can make now for things to do during an earthquake

find safe places in each room, make a plan with others where to meet after the earthquake

### what is the best thing to do if you are indoors during an earthquake

crouch or lie face down under a table or desk in the center of a room

### what is the best thing to do if you are outdoors during an earthquake

lie face down away from buildings, power lines and trees and cover your head with your hands

### S-P time method

the simplest method seismologists use to find an earthquake's epicenter

### seismogram

first step in finding an earthquake's epicenter is to collect several of these from different seismographic stations

### magnitude

the measure of the strength of an earthquake

### 100

is the number of times stronger a 5.0 earthquake is compared to a 4.0 earthquake (in magnitude)

### intensity

is the degree to which people feel an earthquake and the amount of damage it causes

### XII

is the highest intensity level on the Modified Mercalli Intensity Scale

### lowest level of intensity on the Modified Mercalli Scale describes an earthquake

not felt by most people

low

### earthquake kit should contain

flashlight, food that won't spoil, water, first aid kit, radio, fire extinguisher, medicine, batteries, clothes

gap hypothesis

seismic gap

gap hypothesis

### 18

number of major earthquakes with magnitude 7.0 to 7.9 happen on average in the world each year

released

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