Section 1 Where Do Earthquakes Occur? -Most happen on tectonic plate boundaries. -As an effect of plate movement many things called faults exist. -Fault: break in the Earth's crust where blocks of crust slide relative to each other.-this is what makes earthquakes. What Causes Earthquakes? -stress happens when plates move past each other.-when stress occurs deformation happens. -deformation: bending,tilting, and breaking the Earth's crust. Elastic Rebound. -elastic rebound: return of elastically deformed rock to its original shape.(like a stretched rubber band coming to its original form). -during this, energy is released, some of this energy travels through seismic waves. Thus creating an earthquake. Faults at tectonic plate boundaries -Certain types of plate motion happen at different plate boundaries. -Trasform plate motion = strike-slip fault -Convergent plate motion = reverse fault -Divergent plate motion = normal fault How Do Earthquake waves travel? -Seismic waves: wave of energy that travels through the Earth, away from an earthquake in all directions. -waves that travel through the earth are called body waves -waves that travel on Earth's surface are called surface waves. -P wave:wave that makes rock particles move in a back-and-forth direction. -fastest waves,also called primary waves,first to be detected. -S wave: wave that makes particles of rock to move in a side-to-side direction. -also called shear waves,second fastest,cannot travel through the parts of the earth with water,also called secondary waves. -Surface waves: usually the motion is made on the first few kilometers of the crust,similar to S waves from its direction of its movement. Section 2 Earthquake Measurement -Scientists find earthquakes on seismographs. -seismograph: object that finds vibrations in the ground and finds the location and strength of the earthquake. - a seismogram is the finding earthquake motion, this is what is produced by a seismograph. - Scientists use seismograms to find out when an earthquakes first started and to find the epicenter -they find the earthquake tart time by comparing seismograms and looking at the different arrivals of P and S waves. -epicenter : point on Earth's surface above focus. -focus : point along a fault where the first motion of an earthquake happens. -S-P TIME METHOD -simplest method of finding the epicenter RICHTER SCALE -measures strength of earthquakes. MODIFIED MERCALLI INTENSITY SCALE -Numerical scale used with the Roman numerals I-XII to describe how intense the earthquake is, intensity values are higher at the epicenter. Section 3 Earthquake Hazard -a measurement of how likely an area is to have earthquakes is and earthquake hazard. -This is determined by past and present seismic wave activity. -Greater the seismic activity=higher earthquake hazard level. -strength of an earthquake relates to how often they occur. gap hypothesis: hypothesis based on the idea that a major earthquake is more likely to occur along a fault where no earth quakes have occured for a long time. -seismic gaps : area along a fault where few earthquakes have occurred recently but where strong earthquakes have happened in the past. EARTHQUAKE RESISTANCE - Making older structures earthquake resistant is called retrofitting. -A weight that is placed on a building to make the building earthquake resistant is a mass damper. -An areas earthquake hazard level is determined by past and present seismic activity. -Retrofitting includes the things: mass damper, active tendon system, base isolators, cross braces, flexible pipes. -A light earthquake would be more likely to happen near an area where there had not been many earthquakes easily because the ground would be sturdy and nothing has happened in a long time.