21. Death of a Convergent Boundary • Old oceanic lithosphere is more dense than continental lithosphere -- so it sinks lithosphere asthenosphere volcano chain trench
37. Seismograph: The instrument (Apparatus to measure and record vibrations) Seismogram: The actual wiggle (Record of an Earth tremor recorded by a seismograph) What’s the difference between a “Seismograph” and a “Seismogram”?
44. Modified Mercalli Intensity Scale I Not felt II Felt only by persons at rest III–IV Felt by persons indoors only V–VI Felt by all; some damage to plaster, chimneys VII People run outdoors, damage to poorly built structures VIII Well-built structures slightly damaged; poorly built structures suffer major damage IX Buildings shifted off foundations X Some well-built structures destroyed XI Few masonry structures remain standing; bridges destroyed XII Damage total; waves seen on ground; objects thrown into air
Eastern Nebraska 1877 11 15 17:45 UTC Magnitude 5.1 Intensity VII Largest Earthquake in Nebraska This is the largest earthquake known to have originated in Nebraska. Its proposed epicenter lies on the western flank of the Keweenawan mafic belt. Damage was most severe at Columbus, in Platte County, northwest of the epicenter, where the 30-second shock split the courthouse walls in nine places and damaged the schoolhouse walls. Two severe shocks about 350 kilometers west of Lincoln, at North Platte, cracked walls and overturned printing cases. About 200 kilometers north of Lincoln, at Sioux City, Iowa, a high school sustained cracks in a wall. Felt over all or parts of Iowa, Kansas, Minnesota, Missouri, Nebraska, South Dakota, and Wisconsin. Socorro area, New Mexico 1906 11 15 12:15 UTC Intensity VII Largest Earthquake in New Mexico This earthquake, which increased the property damage already sustained at Socorro, was described as the most severe shock of the year. Four rebuilt chimneys were shaken off the Socorro County Courthouse, and two others were cracked severely. Plaster fell at the courthouse, and a cornice on the northwest corner of the two-story adobe Masonic Temple was thrown onto its first floor. Several bricks fell from the front gable on one house. Plaster was shaken from walls in Santa Fe, about 200 kilometers from the epicenter. Felt over most of New Mexico and in parts of Arizona and Texas. Kuril One person injured at Waikiki by a tsunami with a recorded wave height of 34 cm at Honolulu, Hawaii. One parking lot was flooded at Nawiliwili, Hawaii by a tsunami with a recorded wave height of 88 cm. Two docks destroyed and at least one damaged at Crescent City, California by a tsunami with a recorded wave height of 176 cm. Felt at Misawa and Yokosuka, Japan and at Petropavlovsk- Kamchatskiy, Russia. Recorded (2 JMA) in eastern and south- central Hokkaido. Recorded (1 JMA) in western Hokkaido and in Aomori, Iwate and Miyagi Prefectures, Honshu. From Significant Earthquakes of the World 2006 .
Fault Area Approximately: 1200km by 100 km (800 miles by 60 miles)
Good Friday
Picture shows 3 types of plate boundary. Divergent, e.g. mid-ocean ridge. Magma rises from asthenospheric mantle, melts to form new crust e.g. at continental crust -> rifting (many normal faults) Convergent, e.g. oceanic crust subducts (more dense). Subducted crust melts ->magma rises to create volcanoes If continent converging on continent, two buckle into mountain range (too buoyant to be subducted) transform. Two plates slide without creation or destruction of crust - e.g. san andreas transform fault.
Seafloor spreading New crust forms at axis just a few km wide. Slow spreading ridges are narrow and have a deep trough (e.g. mid atlantic) Fast spreading ridges (e.g. east pacific rise) there is no trough and the ridge is wide
For example india crashing into asia. Oceanic crust is consumed. Once the continental crust collides with another continental crust, both are buoyant and neither are subducted. 50 million years this has been happening
And then the continental crust collides. Again, continental crust is too buoyant to be subducted.
Not all transform faults are at sea, the most famous one is san andreas. Crust is neither being created nor destroyed. Also acts as connector in ocean with seafloor ridges
4 cm/yr In 20 million years, LA will be side by side with San Francisco
www001.upp.so-net.ne.jp/ fl-fg/05-01.htm
Put in did you feel it, with website screen shots
Earthquakes less than M=2: are generally not felt Magnitude scales are logarithmic: An increase of 1 unit = 10 times greater amplitude of ground motion up to about a M=7 An increase of 1 unit = 30 times more energy Largest quake ever recorded had a moment magnitude of 9.5 (Chile, 1960)
Richter magnitude scale: A logarithmic scale based on the maximum amplitude of ground motion recorded on a standard seismograph at a distance of 100 km from the earthquake. No upper or lower limit. Saturates above M6 using body waves, and M8 using surface waves. Moment magnitude scale: A logarithmic scale based on the amount of energy released by the earthquake. The magnitude is related to the total fault rupture area times the amount of slip. It can be determined from the distribution of seismic wave frequencies recorded on a seismogram. Energy is a better estimate of earthquake size than the amplitude of seismic waves recorded on a seismograph.
