Earthquakes in the Central United States Larry Braile, braile@purdue.edu, web.ics.purdue.edu/~braile Sheryl Braile NSTA, 2007 St. Louis This PowerPoint Presentation (last modified March 28, 2007): http://web.ics.purdue.edu/~braile/edumod/CUSeqs/CUSeqs.ppt

File to print 11 x 17 size color maps: http://web.ics.purdue.edu/~braile/edumod/CUSeqs/CUSeqsTwoMaps.doc

Ordering Maps from the USGS: Central United States Earthquakes, Product 101503, $7 + S&H (~34.5 – 39.5 deg N, ~93.25 – 87 deg W): http://rockyweb.cr.usgs.gov/outreach/mapcatalog/images/earthquake/ centralregionearthquakes.jpg Central Region USA Earthquakes (Three Centuries), Product 115886, $7 + S&H (34 – 42.5 deg N, 93 – 86 deg W): central_usa_earthquakes_3centuries.jpg http://store.usgs.gov/ USGS store, then “enter usgs store” or, Call 1-888-ASK-USGS, Enter/order by product number.

Using the two Central US earthquake maps… 1. Trace the locations of the major rivers in the area. 2. Describe the pattern of earthquake epicenters on the Central US Earthquakes map. 3. Measure the distance (in km) from the area of greatest earthquake activity to major population centers.

1. Selected Contemporary Accounts of 1811 New Madrid Earthquake Other Resources: 1. Selected Contemporary Accounts of 1811 New Madrid Earthquake http://web.ics.purdue.edu/~braile/edumod/CUSeqs/SelectedAccounts.doc 2. New Madrid earthquake information from Susan Hough, USGS http://pasadena.wr.usgs.gov/office/hough/ 3. Modified Mercalli Intensity Scale: http://web.ics.purdue.edu/~braile/edumod/CUSeqs/EarthquakeIntensity.doc

Seismic Eruption software: http://www. geol. binghamton New Madrid area historical earthquakes files, download from: http://web.ics.purdue.edu/~braile/edumod/CUSeqs/CUSFiles.htm

Using the Seismic Eruption program, we can view the earthquake activity in the New Madrid area through time. We can also use the Seismic Eruption program and the New Madrid data set to calculate a frequency-magnitude (Gutenberg-Richter) relationship that can be used to estimate recurrence intervals for various magnitude earthquakes.

Recurrence Interval for ~M7+ event ~1000 to 1500 years (estimated from these data)

Earthquake Intensity Of the two ways to measure earthquake size, magnitude based on instrumental readings and intensity based on qualitative effects of earthquakes, only intensity can be applied to pre-instrumental earthquakes. The 1931 Modified Mercalli scale used in the United States assigns a Roman numeral in the range I - XII to each earthquake effect. The methodology is simple. At each location assign a numeral to describe the earthquake effect. Contour the zones of similar effect. The earthquake is assumed to have occurred near the region of maximum intensity. The earthquake may be characterized by the largest Roman numeral assigned to it. The problems with intensity are multifold. First, it is a qualitative assessment that measures different phenomena. The lower values address human response to ground motions, the intermediate values characterize the response of simple structures, and the upper values describe ground failure processes. Another problem is that incomplete spatial coverage may lead to a mislocation of the earthquake or an underassessment of its size. This is easily visualized for offshore earthquakes or, in the case of the United States, inadequate population distribution at the time of the earthquake.

Modified Mercalli Scale Average peak velocity (centimeters per second) Intensity value and description Average peak acceleration (g is gravity=9.80 meters per second squared) I. Not felt except by a very few under especially favorable circumstances. (I Rossi-Forel scale) II. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. (I to II Rossi-Forel scale) III. Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibration like passing of truck. Duration estimated. (III Rossi-Forel scale) 1-2 IV. During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing automobiles rocked noticeably. (IV to V Rossi-Forel scale) 0.015g-0.02g 2-5 V. Felt by nearly everyone, many awakened. Some dishes, windows, and so on broken; cracked plaster in a few places; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop. (V to VI Rossi-Forel scale) 0.03g-0.04g

5-8 VI. Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster and damaged chimneys. Damage slight. (VI to VII Rossi-Forel scale) 0.06g-0.07g 8-12 VII. Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving cars. (VIII Rossi-Forel scale) 0.10g-0.15g 20-30 VIII. Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stack, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving cars disturbed. (VIII + to IX Rossi-Forel scale) 0.25g-0.30g 45-55 IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken. (IX + Rossi-Forel scale) 0.50g-0.55g More than 60 X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed, slopped over banks. (X Rossi-Forel scale) More than 0.60g XI. Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. XII. Damage total. Waves seen on ground surface. Lines of sight and level distorted. Objects thrown into the air.

Bolt, Bruce A. Abridged Modified Mercalli Intensity Scale, Earthquakes - Newly Revised and Expanded, Appendix C, W.H. Freeman and Co. 1993, 331 pp. http://mnw.eas.slu.edu/Earthquake_Center/mercalli.html Using contemporary accounts (mostly newspaper articles) we can estimate the Modified Mercalli Intensities (MMI) of ground shaking at various locations from the New madrid events and estimate felt area and magnitude.

Modified from: http://pasadena.wr.usgs.gov/office/hough/dec.gif

Modified from: http://pasadena.wr.usgs.gov/office/hough/dec.gif

Intensity maps comparing intensity of shaking and expected damage for New Madrid and California earthquakes.

Intensity maps comparing intensity of shaking and expected damage for New Madrid and California earthquakes (http://geopubs.wr.usgs.gov/fact-sheet/fs017-03/)

Shake map (from S. Hough, USGS) intensity data for the Dec Shake map (from S. Hough, USGS) intensity data for the Dec. 16, 1811 earthquake.

Shake map (from S. Hough, USGS) comparison for New Madrid and Landers earthquakes.

http://www. eas. slu. edu/Earthquake_Center/SEISMICITY/Street/fig1 http://www.eas.slu.edu/Earthquake_Center/SEISMICITY/Street/fig1.html

Hazard map for the US, (http://geopubs. wr. usgs

Seismograph network installed in 1974. Main trends of epicenters visible after only 2 years. http://web.ics.purdue.edu/~braile/news/midwest.htm

NE-SW and NNW-SSE epicenter trends (faults) are well defined after 10 years. NE extension and other seismicity Visible.

After 20 years of recording, less obvious trends (rift-bounding fault, NE extension, NW trend, SW extension and diffuse seismicity) are recognizable.

New Madrid 1811-1812 Earthquakes 1/23/1812 M7.0 2/7/1812 M7.5 12/16/1811 (dawn) M7.0 12/16/1811 M7.3 After Susan Hough, http://pasadena.wr.usgs.gov/office/hough/scenario2.jpg

Cause of New Madrid Earthquakes? Pattern of epicenters correlates with prominent positive gravity anomaly (caused by high density rocks in crust beneath sediments in the Mississippi Embayment). Gravity anomaly (smoothed) shown by colors and contours.

Gravity anomaly and pattern of epi- centers has been interpreted as being caused by an ancient buried rift complex.

Observed gravity anomalies (indicating that higher density rocks are beneath the surface below the Mississippi Embayment) and interpretive cross section of ancient rift structure.

Block diagram of buried rift structure. http://web.ics.purdue.edu/~braile/news/midwest.htm