Lecture Notes: Earthquakes - Part 2 PDF

Seismograph stations around the world. EARTHQUAKES Studying Seismic Waves SEISMIC WAVE data: ✓ provides information about EARTHQUAKES ✓ provides information about the structure of Earth itself (as previously seen). ✓ enables researchers to identify location of EPICENTER and HYPOCENTER. NOT...

Seismograph stations around the world. EARTHQUAKES Studying Seismic Waves SEISMIC WAVE data: ✓ provides information about EARTHQUAKES ✓ provides information about the structure of Earth itself (as previously seen). ✓ enables researchers to identify location of EPICENTER and HYPOCENTER. NOTE: HYPOCENTER is also referred to as the FOCUS of an EARTHQUAKE. A network of stations monitoring SEISMIC WAVES exists around the globe. 2 Studying Seismic Waves SEISMIC WAVE data: ✓ provides information about EARTHQUAKES ✓ provides information about the structure of Earth itself (as previously seen). ✓ enables researchers to identify location of EPICENTER and HYPOCENTER. NOTE: HYPOCENTER is also referred to as the FOCUS of an EARTHQUAKE. Each red dot is a station monitoring A network of stations monitoring SEISMIC WAVES SEISMIC WAVES/earthquake activity. exists around the globe. 3 Studying Seismic Waves SEISMOGRAPH: ✓ tool that records data about SEISMIC WAVES. ✓ tool that measures SEISMIC WAVES generated by EARTHQUAKES. ✓ tool that detects and records movements of Earth using sensor placed deep in the ground. SEISMOMETER: sensor on a SEISMOGRAPH that detects movements. SEISMOMETER touches rocks in the ground and can therefore sense/detect any vibrations travelling through Earth SEISMOMETER transmits vibrational signals detected up to SEISMOMETER: sensor on SEISMOGRAPH SEISMOGRAPH that detects movements. 4 Studying Seismic Waves GPS SEISMOGRAPH: DATA TRANSMISSION ✓ tool that records data about SEISMIC WAVES. ✓ tool that measures SEISMIC WAVES generated by EARTHQUAKES. ✓ tool that detects and records movements of Earth using sensor placed deep in the ground. COMPUTER/ SEISMOMETER: sensor on a SEISMOGRAPH that detects COMMUNICATIONS EQUIPMENT movements. SEISMOMETER SEISMOMETER touches rocks in the ground and can therefore sense/detect any vibrations travelling through Earth SEISMOMETER transmits vibrational signals detected up to SEISMOMETER: sensor on SEISMOGRAPH SEISMOGRAPH that detects movements. 5 Studying Seismic Waves SEISMOGRAM: Data generated by SEISMOGRAPH;. SEISMOGRAM is data generated by SEISMOGRAPH based on vibrations detected by SEISMOMETER. If no vibrations in Earth, see straight line on SEISMOGRAM. If have vibrations, see “jumps” (increased AMPLITUDE) on SEISMOGRAM. Why 3 lines of data? A SEISMOGRAPH will monitor 3 types of motion: ✓ up/down ✓ East/West ✓ North/South A SEISMOGRAM, generated by a A SEISMOGRAM, generated by a SEISMOGRAPH. Here, p-WAVES and SEISMOGRAPH. Here, SEISMIC WAVES s-WAVES have already been detected. are causing the “jumps” observed. 6  Studying Seismic Waves Waves review: AMPLITUDE of a wave: maximum CREST CREST displacement or height of a wave relative to its equilibrium position (here equilibrium position is the black line). WAVELENGTH of a wave: ✓ distance over which wave shape repeats. TROUGH TROUGH ✓ distance between two CRESTS (i.e., peaks) or two TROUGHS on a wave. Video reviewing AMPLITUDE as (as it relates to TSUNAMIS): https://www.youtube.com/watch?v=2Kos5VrtTtA 7 Studying Seismic Waves A simpler SEISMOGRAPH: Lab scale SEISMOGRAPHS are simpler and record data HEAVY MASS with pen at the end right onto a roll of paper. (does not move). Paper is constantly passing/rolling under a pen so that PAPER (being rolled in direction of blue arrow). vibrations can be recorded. A hanging (often on a spring) heavy mass with a pen at end does not move/stays in place regardless of vibrations. Earth motion due to EARTHQUAKE. Rest of unit moves when SEISMIC WAVE vibrations felt. NOTE: Paper moves with the SEISMOGRAPH, so we A simple SEISMOGRAPH. observe waves as jumps (increases in AMPLITUDE) on our paper (i.e., on our SEISMOGRAM). 8 Studying Seismic Waves To determine location of EPICENTER: measure and compare arrival times of SEISMIC WAVES at different locations/stations monitoring SEISMIC ACTIVITY. To determine location of HYPOCENTER: more complicated (must analyze SEISMIC WAVE patterns -use SEISMIC TOMOGRAPHY). SEISMIC TOMOGRAPHY: An imagining technique using SEISMIC WAVE data to create computer generated 3- dimensional images of Earth’s interior. SEISMIC TOMOGRAPHY also provides information about Earth’s composition as shown in this brief video: SEISMIC TOMOGRAPHY provides https://www.youtube.com/watch?v=Hrto0nIP8nk information as to what lies beneath! 9 Recording Earthquakes EARTHQUAKES cause a release of energy that makes ground vibrate. Energy travels from HYPOCENTER in form of SEISMIC WAVES. Not all EARTHQUAKES are the same – some are extremely destructive while others are only detected by sensitive SEISMOMETERS. We measure different aspects of an EARTHQUAKE, namely its MAGNITUDE and INTENSITY. INTENSITY: measure of shaking and damage caused by EARTHQUAKE INTENSITY will vary from LOCATION to LOCATION. MAGNITUDE: Largest recorded EARTHQUAKES have had a magnitude of approximately 9. But what does that mean? 10 Recording Earthquakes MAGNITUDE: ✓ most common measure of EARTHQUAKE’s size ✓ measured at EARTHQUAKE’s source ✓ a single number is reported (no matter where we are relative to EARTHQUAKE and what we feel) RICHTER SCALE: ✓ outdated method for measuring magnitude ✓ developed by Charles Richter in 1932 ✓ hypothetically scale has NO upper or lower limit ✓ Practically scale ranges from 1 to 10 (with 10 being most powerful EARTHQUAKE) 11 Recording Earthquakes MAGNITUDE: ✓ most common measure of EARTHQUAKE’s size ✓ measured at EARTHQUAKE’s source ✓ a single number is reported (no matter where we are relative to EARTHQUAKE and what we feel) RICHTER SCALE: ✓ outdated method for measuring magnitude ✓ developed by Charles Richter in 1932 ✓ hypothetically scale has NO upper or lower limit ✓ Practically scale ranges from 1 to 10 (with 10 being most powerful EARTHQUAKE) 12 Recording Earthquakes RICHTER SCALE is LOGARITHMIC! In other words: Each time scale value goes up by 1 unit (e.g., from 1 to 2 or 5 to 6), MAGNITUDE of EARTHQUAKE is 10x bigger! Based on this: MAGNITUDE 2 is 10x BIGGER than MAGNITUDE 1 MAGNITUDE 3 is 10x10 or 100x BIGGER than MAGNITUDE 1 MAGNITUDE 4 is 10x10x10 or 1000x BIGGER than MAGNITUDE 1 MAGNITUDE 5 is 10x10x10x10 or 10,000x BIGGER than MAGNITUDE 1 etc… If MAGNITUDE ≥ 8, dealing with a huge EARTHQUAKE that can destroy communities near EPICENTER. If MAGNITUDE ≤ 2.5, EARTHQUAKE usually not even felt by humans, just detected by SEISMOMETERS. 13  Richter Scale SEISMOGRAM reading Calculation of RICHTER SCALE MAGNITUDE involves: ✓ measuring largest signals (greatest AMPLITUDES) on SEISMOGRAM Time between s ✓ measuring time difference between arrival of and p-WAVES p-WAVES and s-WAVES ✓ accounting for distance from EARTHQUAKE source Magnitude Amplitude Distance from EARTHQUAKE source 14 Moment Magnitude Scale: The New Standard RICHTER SCALE MAGNITUDE: ✓ underestimates energy released by EARTHQUAKES with MAGNITUDES > 6.5. ✓ unknown to many, it has now been largely replaced by the MOMENT MAGNITUDE SCALE. The MOMENT MAGNITUDE SCALE is described here: https://www.youtube.com/watch?v=nl9jiubdlXU 15 Other Earthquake Sources Not all EARTHQUAKES are the result of TECTONIC PLATE collisions. Other than TECTONIC EARTHQUAKES we also encounter: VOLCANIC EARTHQUAKES: Earthquakes that occur in parallel with volcanic activity. COLLAPSE EARTHQUAKES: Smaller earthquakes caused by subterranean/underground collapse of caves or mines. EXPLOSION EARTHQUAKES: Earthquakes caused by explosions of nuclear or chemical devices (e.g., bombs). 16  Notable Earthquakes: In-Class Discussion Using your phone (and with a partner), please look up a notable EARTHQUAKE in the time permitted. Be ready to share information about this Earthquake with the class. Look for information such as: Location Date Magnitude Casualties Damage Caused Rescue Efforts 17 Predicting Earthquakes and Tsunamis Even with today's advancing technology, predicting when EARTHQUAKES will occur remains a challenge. There are many variables to consider. Here is an interesting video discussing this! https://www.youtube.com/watch?v=jhRuUoTnA6g Finally, volcanoes can also trigger TSUNAMIS. Here is an interesting video describing this phenomenon: https://www.youtube.com/watch?v=Wx9vPv-T51I&list=PLJicmE8fK0Ei3dAErHrPBfzRpmFDr4vsy 18  Thank you for listening! Les Eboulements, in Charlevoix Quebec experienced a powerful earthquake in February, 1663!