The earthquake of September 2, 1999, in northern Illinois : big lessons from a small earthquake

32 Pages·2001·1.7 MB·English

by  Larson, Timothy H

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r&/0 (53
EG 153
The Earthquake of September
2, 1999,
Northern
in Illinois:
Big Lessons from a Small Earthquake
Timothy H. Larson
Environmental Geology 153 2001
George H. Ryan, Governor
Department ofNatural Resources
Brent Manning, Director
ILLINOIS STATE GEOLOGICALSURVEY
WilliamW.Shilts, Chief
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1
The Earthquake of September
2, 1999,
Northern
in
Illinois:
Big Lessons from a Small Earthquake
Timothy H. Larson
Environmental Geology 153 200
George H. Ryan, Governor
Department ofNatural Resources
Brent Manning, Director
ILLINOIS STATE GEOLOGICALSURVEY
WilliamW. ShiTts, Chief
615 E. PeabodyDrive
Champaign, IL61820-6964
[phone]
Digitized by the Internet Archive
2012 with funding from
in
Urbana-Champaign
University of Illinois
http://archive.org/details/earthquakeofsept153lars
Contents
Abstract 1
Introduction 1
LocalGeologyand Its InfluenceonEarthquakes 3
GeologicStructures 3
EffectsofSoils 6
Intensity:DocumentingtheEffectsoftheEarthquake 8
TheISGSIntensitySurvey 8
TheUSGSIntensitySurvey 9
Combining BothSurveys 9
SurveyResults 10
Conclusions 12
Acknowledgments 13
References 13
Appendices
1 ISGSintensitysurveyaftertheSeptember2, 1999,earthquake 15
2 SummarylistingofISGSintensitysurveyresultsgatheredbytown 16
3 USGSintensitydataforthenorthernIllinoisearthquakeSeptember2, 1999 18
Figures
1 SimplifiedwaveformsoftheSeptember2, 1999,earthquakerecordedatDeKalb,Illinois,
St.Louis,Missouri,andCarbondale,Illinois 2
2 NorthernIllinoisearthquakeswithyearofoccurrenceandmagnitude 2
3 StructuremapdrawnonthetopoftheFranconiaFormation 4
4 DiagrammaticwesttoeastcrosssectionthroughtheNorthAmericanPlate 4
5 Faultmotionofthe 1972 earthquake,measuredfromanalysisofseismicrecords 5
6 Buriedbedrocktopography 6
7 IsoseismalmapoftheSeptember2, 1999,earthquake 9
8 IsoseismalmapoftheSeptember2, 1999, earthquakeoverlainonamapofsoilthickness 10
9 Isoseismalmapofthe 1972earthquakewiththe1999epicenterincluded 11

Abstract km2 (400mi2) areaofMMI IVsur- cline.Althoughoneearthquakeepicen-
m roundedtheselocations.Localge- ternearthePeruMonoclinemightbe
Asmallearthquake,magnitude b3.5, ologywasanimportantfactorin consideredcoincidental,thetwoepicen-
joltednorthernIllinoisat11:17A.M. theintensitypattern.Earthquakein- ters, takentogether,maysuggestthe
CDT(16:17:29.7UTC)onSeptember2, tensitywasgreaterinareasunder- possiblereactivationofaPaleozoic
1999.Theepicenterwaslocatednear lainbythicksandandgraveldepos- structurewithintheNorthAmerican
thevillageofAmboy, LeeCounty, at its,eventhoseburiedbysubse- midcontinent.
laantditautdean41e.s7t3i°mNaatneddldoenpgtihtuodfe58k9m.4(03°W qunudeenrtlgaliancibaylatchtiinvigtlya,ctiahladnriifntaorveears Twostepsarerecommendedtoincrease
mi).Theearthquakewasfeltoveran bedrock. theearthquakepreparednessofnorth-
areaofabout 10,400km2 (4,000mi2 ernIllinois:
),
inonicsluadnidngthpearitmsmoefd1i1atcoeulnytaidejsaicneInltli-re- Aelatrhthoquugahksemaislsliignnimfaigcnanittbudeec,autshiesit 1. Ccaotnisoindoefrstehiesemfifcecwtasvoefssowihleamnpldief-i-
gionsofWisconsinandeasternIowa. isthesecondinstrumentallydocu- signingandretrofittingstructures
Withintwoweeksoftheevent,two mentedearthquakelocatedon,or builtonthickalluviumorglacial
separateintensitysurveyswereiniti- verynear, thePerumMonocline. In sedimentsinnorthernIllinois.
atedbytheIllinoisStateGeological 1972,amagnitude b4.6earth-
SurveyandtheU.S.GeologicalSurvey quakeoccurredabout 16km (10 2. Investigatethepossiblelinkbetween
mi) southeastofthe 1999earth- thesetwoearthquakesandthePeru
toinvestigatetheeffectsofthisearth-
quake.ObservedModifiedMercalli quake.Afocalmechanismsolution Monoclineandtheimplicationfor
Intensityreachedamaximumvalueof fromthe 1972earthquakeisconsis- seismichazardinthisarea.
MMIVintwosmalllocationswestof tentwithstrike-slipmovementpar-
theepicenter.Anasymmetrical1,000 alleltothetrendofthePeruMono-
Introduction severallocationswerecompared, reportedinnorthernIllinois;allbutone
and theearthquake'sepicenterwas (DuPageCounty 1985) occurredbefore
Whenasmallearthquakerattled plottedatapositionabout6.5km(4 reliableseismologicalinstrumentation
acrossnorthernIllinoisjustbefore mi) westofthevillageofAmboy waspresentinthearea.Thelocationsof
lunchonThursday September2, (about24km[15mi] south-south- theseearlierearthquakesarenotknown
1999,thepopularresponsewasfirst eastofDixon) atlatitude41.731°N, verywell. Reportsofhowstronglythe
surprise,thendisbelief,followedby longitude89.398°WFocaldepthwas earthquakeswerefeltatvariousloca-
curiosity.Becauseearthquakesinthis estimatedtobeabout5km (3mi). tionsaretheonlyrecordsoftheevent.
partoftheworldarerare events, the Thetimeoforiginwasfixedat 11:17 Tryingtodeterminethepointoforigin
widelyfelt,single,sharpjoltfromthis A.M.CDT,andthemagnitudewas fromthesereportscanbeproblematic.
earthquakegeneratedconsiderable measuredatm 3.5 (information Forinstance, thelargest earthquake
b
localinterest.Giventhenoveltyofthe fromNationalEarthquakeInforma- reportedin northern Illinois, withan
eventandtheimagesofdevastation tionCenter,Boulder,Colorado). estimatedmagnitudegreaterthan5,
wroughtbyamajorearthquakethat Unfortunately,thesignalsfromthis occurred in 1909. Itcausedwide-
occurredinTurkeylessthanamonth earthquakeweretooweakandthe spread, althoughminor,damagepar-
beforeonAugust 17th,thiscuriosityis numberofrecordinginstruments ticularlyintheFoxRivervalleyfrom
quiteunderstandable.Thisearthquake toofewtoprovideadditionaldetails JoliettoElgin. Evenafterreviewingdoz-
isscientificallysignificantnotbecause onthesourcemechanismofthe ensofnewspaperreports,Udden,who
ofitssize,havingamagnitudeofonly earthquake. However, becauseof actuallyexperiencedtheevent,wasnot
m
b3.5,butbecauseofitslocationand thera—rityofthisevent, thesebasic abletoestablishapointoforigin(Udden
thesubtlevariationsintheeffectsof facts location,origintime,and 1910). Figure2showsthisearthquakein
—
theearthquakewavesastheypassed size arevaluablepiecesofinfor- easternOgleCounty,butothermaps
throughtheregion. Lastingonlyafew mationthatcanleadtoabetterun- haveshownitasfarawayasnortheast-
shortseconds,thisminorearthquake derstandingofearthquakesinthis ernWinnebagoCounty(Heigoldand
leftarecordthatcan providesome area. Larson1990) andnorthernWillCounty
importantinsightsintopresent-day (StoverandCoffman1993).
tectonicprocessesandfutureseismic Thepopularnotionthatnorthern
riskinnorthernIllinois. Illinoisisimmunetoearthquakesis Basedonpastearthquakes, riskfrom
notcompletelytrue. Earthquakes earthquakedamageinnorthernIllinois
Althoughminusculeincomparisonto innorthern Illinoisare rare but islow, butnotzero. Frankeletal. (1996)
contemporarycatastrophicearth- notuniqueevents (fig.2).TheSep- calculatedtheprobablemaximum
quakesinTaiwan(Mw7.6) andTurkey tember1999earthquakeepicenter earthquake-relatedgroundvibrations
(Mw7.4),theSeptember1999northern isapproximately11km(7mi) thatmightoccurovera50-yearperiod.
Illinoisearthquakehadsufficienten- north-northwestoftheepicenterof Theyestimatedthatthereisa2%chance
ergytobedetectedbymanyseismo- anm 4.5earthquakethatoccurred thatslightlydamagingvibrations(hori-
logicalobservatoriesintheMidwest onSebptember15, 1972.Several zontalaccelerationsexceeding8%of
(fig. 1).Instrumentalreadingsfrom otherminorearthquakeshavebeen gravity)mightoccursometimewithin
linois State Geological Survey Environmental Geology 1 53 1
De Kalb wave
(distance 60 km)
St. Louis 100 seconds
(distance 450 km)
minute
1
P waves notvisible
oonn tthhiiss ttrraaccee
|| A A i
Carbondale
(distance 500 km) Time: 1619 UTM (1119 Central)
Figure 1 Simplified waveforms of the September 2, 1999, earthquake recorded at De Kalb, Illinois, St. Louis, Missouri, and
Carbondale, Illinois. The De Kalb waveform (top) was redrawn from a seismograph recorded at Northern Illinois University. The
horizontal axis for this waveform is graduated in 100-second time units. The St. Louis waveform (center) was redrawn from the
daily seismograph recorded at St. Louis University and obtained from their Web site. This is a vertical-component record. The
Carbondale waveform (bottom) was redrawn from the daily seismograph recorded at Southern Illinois University and obtained
from the St. Louis University Web site. This is a horizontal-component record. The St. Louis and Carbondale records are shown
at approximately the same scale with 1-minute time units correlated to the Universal Time Standard (UTC). Surface waves ac-
counted for most of the vibrations recorded at all three sites. The onset of the S wave is obscured by instrument noise on
the De Kalb record. Possible P wave arrivals lead the S wave arrival on the St. Louis record by about a minute. P wave arrivals
are not visible on the Carbondale record.
JODAVIESS STEPHENSON WINNEGABO BOONE MCHENRY
1907 1912
• 3.2 3.6*
1947
3.8
CARROLL OGLE
DEKALB KANE J] COOK
1928 1909
• 3.5 5.1 •
^~V-L
WHITESIDE
LEE
1999
1909* ®
3.5
4.0
1972
4.5 •
LASALLE
HENRY BUREAU
GRUNDY
KANKAKEE
1942
KNOX
4.0
MARSHALL LIVINGSTON
STARK
IROQUOIS
PEORIA
WOODFORD
Figure 2 Northern Illinois earthquakes with year of occurrence and magnitude. Data are from St. Louis University Earth-
quake Center.
Environmental Geology 1 53 linois State Geological Survey
that period at Rockford, Dixon, or and, asyet, noearthquakeshavebeen west-trendingstructures,suchasthe
Sterling. Inthiscalculation,theyas- conclusivelylinkedtoanyofthem PlumRiverFaultZoneinnorthern Illi-
sumedthatnoearthquakeinnorthern (Nelson 1995).Infact,earthquakesin nois (fig. 3), are not known to be ac-
IllinoiswouldexceedMw6.5.Thisis continentalinteriorsaroundtheworld tive inthe modernCentralNorth
onlyslightlymoreconservativethan are rare and difficult to explain American stressfield (Zobackand
them 6.1 maximumearthquakeesti- (Johnston 1989). Onelikelyexplana- Zoback1981).Structuresalignedeither
b
matedbyNuttliandHerrmann (1978). tionforearthquakesinthecentral northwest-southeast,northeast-
Althoughtheprobabilityofsuchan UnitedStatesisthattheyoccuratweak southwest, oreven north-south are
earthquake occurringislow (recur- zonesintherigidlithosphere (fig.4) as more likely to spawn earthquakes in
renceintervalestimatedbyNuttliand itisbeingpushedacrosstheasthenos- Illinois. Ofthesefavorablyoriented
Herrmann [1978] at 1,000years), it phereoftheearth (ZobackandZoback structures, theSandwichFaultZoneis
wouldbestrongenough to cause mod- 1981,Carlsonetal. 1983).Ancientfolds the mostprominent in termsofextent,
eratedamageintheepicentralregion. orfaults, formed inthelithospheric butthePeruMonoclinemayhave
platebyancientstresses, arenow greaterverticaldisplacement (see
Local Geology and Its zonesofweakness inthecrust thatare Nelson 1995forsummaryandbibliog-
more prone to fracturingthan are raphy).
Influence on Earthquakes
ointghetroloocccautri,ontsh.eIonldorsdtreurctfuorrefsrmacutsutr- ThePeruMonocline(fig.3) isa 100km
GeologicStructures Therearefew (65mi)long,northwest-southeastward-
bealignedsothatthepredominant
geologicstructuresinnorthernIllinois northeast-southwesttrend ofthe mod- trendingfoldbelt inwhich therocks
thatcouldcauseearthquakes (fig.3), dip steeply to the southwest into the
ern stressfield cutsacross them. East-
Earthquake Magnitude: In recent years, a new type of magni- needed to convert the observed
How Big Was It? tude has been defined that attempts to rrtbL,g values to Mw values. Two con-
relate the size of the earthquake to the versions are illustrated using for-
The size of an earthquake is nor- seismic moment or energy released mulas given by Boore and
mally reported as a value called by the quake. The moment magnitude Atkinson (1987) (M and
tmaakginnigtutdhee,cwohmimcohnislodgeatreirtmhimneofdtbhye t(hMeofrauMltw)thtaatkersupitnutroedacacnoduntthethaemsoiuzentof JboyhHnastromnse(n19e9t6)al.((M1w(*B9A9))9))a.sThreepoorbt-ed
largest ground motion recorded of movement on the fault (Bolt 1993). served m value is slightly greater
tdyupriengoftsheeisarmriicvalwaovfeaapnardtiacpupllayring Nneoirtmhaelrlyofobtsheersveabtlweo fpoarrtahmeetsemrasllisto tehaarnthMquwafkboeLrgssmbaultlistommuocdherlaetsse than
taostthaendeapricdenctoerrr.ecEtaiornthfqouradkiestmaangcnei- moderate earthquakes common in the Mw for large earthquakes.
central United States, so formulas are
tudes are generally called Richter
magnitudes for the seismologist
10
who first used the measurement.
However, there are many variations bodywave magnitude vs. moment magnitude
depending on the type of seismic
wave being measured. The original
Richter magnitude (also called the
8-
local magnitude, M did not specify
L)
a particular type of seismic wave
and is not used very much any- o
more. More frequently, magnitudes 3
c
are based on P body waves (m
and surface waves (M (Bolt 19b9),3). 0E3 6-
s)
In the central United States, a hy-
0)
brid-type of magnitude using short- Eo
period surface waves (mbLg) is in E
common usage. Because the fre-
4-
quency content of these waves is
more like body waves than usual
long-period surface waves, this
magnitude has always been classi- conversion relationshipsfrom Harmsen etal. 1999 1:1
fied as a type of body wave magni-
tude (Nuttli 1973). Unless otherwise
noted, this type of magnitude is
used in this report. body-wave magnitude (mb
linois State Geological Survey Environmental Geology 1 53
200 400 100 -200
Plum River Fault Zone-
Des Plaines
Disturbance
50 km
M
1999 epicenter
W
1972 epicenter
Figure 3 Structure map drawn on the top ot the Franconia Formation (Nelson 1995) with epicenters of 1999 and 1972 earthquakes.
Elevations are given in feet.
continent midcontinent mid-ocean
arthquake ocean basin ridge
thin organicnrnst -, lithosphere
(crust andtopmost
"plate is "pushed" away layerof mantle)
•from ridge1
"Moho" (boundary "."..".
• '..".". asthenosphere
between crust and mantle)
(upperpartof mantle)
."."....'.•..*.
old faultorsuture ".".".".".".".".".".
.n"ow.'we.a"k.z.o"n.e.in"c.r'us.t'." ..".."..". upwelling heatfrom
"
."..".'....."."...".".... deepwithin mantle
drives plate motions
Figure 4 Diagrammatic west to east cross section through the North American Plate. The continental plate is pushed
westward by the pressure from upwelling magma along the mid-Atlantic ridge. The rigid plate formed from the crust
and topmost layer of the mantle slides along the top of the mantle. Earthquakes sometimes occur within the interior of
the plate when stress builds at weak zones caused by old faults.
Environmental Geology 1 53 linois State Geological Survey