770 likes | 776 Views
Learn about the definitions, types, measurements, and risks of earthquakes, with a focus on seismic activity in Oklahoma. Discover the historical earthquakes in the area, potential impact scenarios, and how to respond in case of a tremor.
E N D
Earthquakes:There’s a whole lotta shakin’ goin’ on Dr. William D. (Bill) Underwood Chesapeake Energy Chair of Geosciences Ok. School of Science & Math.
Definition An earthquake is a sudden movement of the earth resulting from abrupt release of accumulated strain. Earthquakes are classified according to their depth. Shallow < 60 km Intermediate < 300 km Deep > 300 km (sometimes > 450 km)
Wave Types • Surface waves • Travel at interface • Love waves • Rayleigh waves • Eg ocean waves • Body waves • P-waves • S-waves
Seismograms 3 seismometers used to measure 3 components (x, y, z)
Fault Types • Strike-slip Fault • Lateral motion • Normal Fault • Extension • Reverse Fault • Compression • Thrust Fault • Low-angle reverse fault
Strike-slip Fault Left-lateral Right-lateral
San Andreas Fault (r-l) Miller
Normal Fault Miller
Thrust Fault Maher
Earth Structure Shows P-waves No S-waves through core
Oklahoma Let’s look closer to home USGS
Oklahoma Jones January 15, 2010
Oklahoma Where the people are
Oklahoma Prague Nov. 5, 2011 M 5.6
Oklahoma Who felt it?
OklahomaNovember 5, 2011 • M 5.6 main shock at 10:52 PM • M 4.7 foreshock at 2:12 AM • Hundreds (thousands?) of aftershocks • Felt over a wide area • No loss of life; few (no?) injuries • Little damage to property • Tremendous excitement (and anxiety)
OklahomaNovember 5, 2011 • Along a known fault (Wilzetta Fault) of a known tectonic feature (Seminole Uplift) • In basement rock, well below oil activity • Injection is at very low pressures • Major faults have been know in recent geologic past (e.g. Meers) • Mid-continent quakes studied < 200 yrs
Alaska, 1964 Molnia
San Francisco1906 USGS
Sumatra2004-12-24 Landslide Dam USGS
New Madrid cf. San Francisco Steven Dutch, UWGB Steven Dutch, UWGB
Mercalli Scale • Giuseppe Mercalli, 1884 • Subjective • Measures damage • Modified to modern usage http://en.wikipedia.org/wiki/Mercalli_intensity_scale
Richter Scale • Replaced Mercalli scale • Charles Richter, 1935 • Logarithmic measure of amplitude • Each number 10x previous • Each number 30x previous energy • Measured from instruments • Mostly objective http://en.wikipedia.org/wiki/Richter_magnitude_scale
Probability In the next 50 years (USGS): • 1811 – 1812 magnitude (7.5 – 8.0) • 7 – 10 % • 6.0 or greater • 25 – 40%
In Oklahoma • Expected (mb 6.0): • Mercalli IV to V • Likely (mb 6.6): • Mercalli V to VI • Possible (mb 7.0): • Mercalli VI to VII • Worst-case (mb 7.4): • Mercalli VII to VIII
Expected (6.0) • Intensity IV to V • Felt by all, few or no injuries • Rumbling, thunderous sounds • Described as "strong" • Hung objects swung, small objects shift • Trees, buildings sway • Vibrations like light truck • Plaster cracked
Likely (6.6) • Worse in eastern Oklahoma • Some structural damage • Many run outside; few minor injuries • Trees, bushes, buildings shaken strongly • Objects off shelf; large furniture disturbed • Plaster falls, chimneys cracked • Small church bells ring
Possible (7.0) • Similar to 5.6 in Prague, Nov. 2011 • Reaction important (drop, cover, hold on) • General alarm and fright; injuries probable • Free-standing masonry walls crack • Well-built structures damaged • Tall chimneys broken • Landslides; springs and wells change
Worst case (7.4) • Panic widespread, injuries common • Reaction critical (drop, cover, hold on) • Free-standing walls & external masonry fall • Ordinary, substantial buildings damaged • Waves seen on ground surface • Telephones out of service • Chimneys, factory stacks, monuments fall