GEOL 101 1nd Edition Lecture 27 Outline of Last Lecture I. Consequences of Climate ChangeII. The Changing FutureOutline of Current Lecture I. EarthquakesII. SeismologyIII. Seismic WavesCurrent LectureEarthquakes-An earthquake is the vibration or shaking of the earth produced by the rapid release of energy-This energy radiates outward in all directions from a central point – the focus- The focus (or sometimes called the hypocenter) is usually at some depth below the surface- The energy is released in the form of waves- The point on the surface directly above the focus is called the epicenter-Earthquakes tend to occur along plate boundaries or faults. -As rocks on both sides of a fault slide past each other, they build up tremendous amounts of stress and friction- This causes potential energy to be stored in the rocks-At first, the rocks bend to accommodate this stress-Eventually the stress becomes too great and the rocks snap, releasing all of the stored energy in the form of earthquake waves****stick analogy below***These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Seismology-Geologists who study earthquakes are most interested in the energy waves that are produced- These waves are called seismic waves, and the science is referred to a seismology-Seismology actually dates back 2000 years to the Chinese, who developed the first seismometer, which recorded the initial direction of motion-Modern seismometers (or seismographs) record the earthquake waves on to paper-Seismographs contain a weight that is freely suspended from a support that is attached to the bedrock- There is also a pen attached to the weight-Within the seismograph there is also a spool of calibrated paper that is rotating -During an Earthquake, the mass remains stationary due to inertia, while the rest of the seismograph moves with the rock -The free weight with the pen records the earthquake waves onto the spool, producing a seismogram-Today most seismometers are digital, and relay the information back to computers at a seismic lab- These seismic stations are placed everywhere, even in areas that are not seismically active. Seismic Waves-There are three kinds of seismic waves that a seismograph records:- P-waves - S-waves- Surface waves (L-waves)- These waves all travel at different velocities, allowing seismographs record each of them-The time difference between the arrivals of each of the waves is used to locate the epicenter-P-waves:- (Primary waves) are the fastest of waves, and therefore arrive first at the seismic station- Move in a push-pull motion (compress-expand)- Can travel through solids, liquids, and gases.-S-waves:- (Secondary waves) are slower than p-waves and more arrive second at the seismic station- Move in an up-down motion- Can travel through solids, but NOT liquid or gases-Surface waves:- Surface waves are the slowest of the three waves and arrive last at the seismic station- The motion of surface waves tends to be much more complex- There is usually some amount of horizontal and vertical movement- Surface waves cause the most damage to
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