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