EARTHQUAKES Earthquakes Where Earthquakes Occur How Earthquakes Happen Volcanoes and Earthquakes.
Teaching about New Madrid earthquakes: science …...2.The 1811-1812 earthquakes 3. Disasters,...
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Teaching about New Madrid earthquakes: science and hazard Illinois Earthscope Teachersʼ Workshop Seth Stein Northwestern University
Transcript of Teaching about New Madrid earthquakes: science …...2.The 1811-1812 earthquakes 3. Disasters,...
Teaching aboutNew Madrid
earthquakes:science and hazard
Illinois EarthscopeTeachersʼWorkshop
Seth Stein Northwestern
University
Why this is a exciting problemWhat we knowWhat we donʼt
What we suspectHow we try to learn more
“Half of what we will teach you in the next fewyears is wrong. The problem is we donʼt know
which half”Medical school dean to incoming students
1. Introduction to the NMSZ2. The 1811-1812 earthquakes3. Disasters, pseudodisasters, and critical thinking4. How the ground shakes5. How earthquakes work6. Earthquakes that shouldnʼt happen7. What's going on at New Madrid?8. Faults switching on and off9. As dangerous as California?10. What to do?
1900-2002
PACIFIC
NORTH AMERICA
New Madrid seismic zone
M 7 earthquakes in1811-12Small quakescontinue (M>6about every 175years) with littledamageBig ones mighthappen againQuestions: why,when, howdangerous
Type example of continentalmidplate seismicity
DD 10.1
Midwest earthquakes 1975-2008
DD 1.2
Concentration aroundNew Madrid, mostlyaftershocks definingfaults that broke inlarge 1811-12 eventsLesser concentration inWabash Valley seismiczoneSurrounded by diffuseregional “cloud”
NMSZWVSZ
20081968
EARTHQUAKE MAGNITUDEEarliest measure ofearthquake size
Dimensionless numbermeasured fromseismogram variousways, including
ML local magnitudemb body wave magnitudeMs surface wavemagnitudeMw moment magnitude
Mw directly tied tophysics of faulting
R. Aster
DD 8.3
Biggerearthquakesinvolve more slipon larger faults
DD 8.4
IRIS
DD 8.6
Bigger earthquakes are less frequent
Earthquakes of a given magnitude are about 10 timesless frequent than ones a magnitude unit larger
How often do New Madrid zone earthquakesoccur?
DD 8.7
Log-linear plotlog N = a - bM
where N isnumber of
earthquakes withmagnitude >= M
One M > 5 aboutevery 20 years
One M>6 aboutevery 175 years
1900-2002
PACIFIC
NORTH AMERICA
Activity 1.1California vs New
Madrid
DD 10.1
Since 1816southern Californiahas had about 180earthquakes with Mgreater than orequal to 6 and 25with M greater thanor equal to 7Calculate howfrequent M5 andM6 are andcompare them toNew Madrid
Largest in past century, 1968(M 5.5) southern Illinois
earthquake, caused no fatalities.Damage consisted of fallen bricksfrom chimneys, broken windows,
toppled television aerials, andcracked or fallen brick & plaster.
April 2008 M 5.2
In West Salem, a few miles from the epicenter of Friday's quake, some residents took theuproar in stride. Bill Harrison, 76, who's lived through a few similar temblors, calmly waved atcars as he sat in front of a window shattered by the morning rumble. "It's not too much to getexcited about," Harrison said. "The ground's shook before and it'll shake again." (Chi. Tribune)
MODIFIEDMERCALLIINTENSITY
SCALE
Describesshaking & its
effectsProportional to
groundacceleration (g)Estimated for
historicearthquakes
from accountsof what
happened
Activity 1.2: Did you feel it?
Where do you live?Did you feel the2008 earthquake?Describe theshaking you feltand its effectsAssign an intensityvalue and label iton the map
April 2008M 5.2
Intensitymap
USGS/FEMA claim: New Madrid as or morehazardous than California
Buildings should be built to same standards
Frankel etal., 1996
Given cost, important to decide if this makes sense
