EARTHQUAKE SUMMARY MAP XXXU.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

DISCLAIMERBase map data, such as place names and politicalboundaries, are the best available but may not be current or may contain inaccuracies and thereforeshould not be regarded as having official significance.

Eagle

Bay

fault

Faults of Brimstone Basin area

Mirror Plateau

faults

Shoshone Lake

Yellowstone Lake

Old Faithful Geyser Basin

Boundary of640,000 year old caldera

Sour Creek dome faults

1998

2002

1999

2000

2002

1999 1995 1996

20062006

1995

2008Mallard Lakedome faults Elep

hant Back fau

lt zone

110°10'

110°10'

110°20'

110°20'

110°30'

110°30'

110°40'

110°40'

110°50'

110°50'

44°40' 44°40'

44°30' 44°30'

44°20' 44°20'

MONTANA

IDAHO

WYOMING

HebgenLake

YellowstoneLake

Epicentral Area

Yellowstone National Park

JacksonLake

AbsarokaRange

MadisonRange

AbsarokaRange

1975

1959

1959

1959

19591959

1947

110°

110°

111°

111°

112°

112°

45° 45°

44° 44°

Yellowstone Lake Earthquake Swarm of December 2008-January 2009

0 10 20Km

Projection Albers Equal Area, Central Meridian 111°W

Epicentral Area

WYOMING

MONTANA

IDAHO

Helena

Boise

110°

110°

115°

115°

45°45°

DATA SOURCESEARTHQUAKES AND SEISMIC HAZARD Univ Utah Seismograph Stations (1984-2009) USGS, National Earthquake Information Center IASPEI, Centennial Catalog (1900-1999) and extensions (Engdahl and Villaseñor, 2002) Global Seismic Hazard Assessment Program Seismicity of the United States, 1568-1989 (Stover and Coffmann, 1993) FAULT DATA Quaternary Faults and Folds Database (2006) BASE MAP NIMA and ESRI, Digital Chart of the World USGS, EROS Data Center NOAA GEBCO and GLOBE Elevation Models

0 50Km

Scale 1:10,000,000

Tectonic Setting

Seismic Hazard

Epicentral Region

Volcano-Tectonic Summary

Yellowstone National Park is located a top aQuaternary silicic volcanic system that ventedin three giant caldera-forming eruptionsbetween 0.64 and 2.1 million years ago. Thethree major eruptions resulted in the 60 km by40 km Yellowstone caldera at the center of thepark. Subsequently, more than 30 smallerrhyolite flows, as young as 70,000 years old,were deposited and locally cover theYellowstone Plateau. The modern volcaniclandscape is superimposed on pre-existingtopography of north-south trending mountainranges and intervening valleys formed as theresult of large magnitude earthquakes on normalfaults; some of the most notable being the Tetonfault, Hebgen fault (the source of the deadly1959 M7.5 earthquake), and Madison faults. Nodoubt large mountain blocks bounded by faultsexisted prior to the volcanic activity but theyhave been modified extensively by the morerecent volcanic activity. Nonetheless the pre-existing faults, confirmed by the alignment ofcontemporary seismicity, produced zones ofcrustal weakness that also function as conduitsfor post-caldera magmatic flows.Seismic tomographic imaging using localearthquakes as sources has revealed a lowseismic velocity body identified as an theYellowstone’s ìmagma chamberî that extendsbeneath the Yellowstone caldera at depths of 8

to 16 km with 8-15% partial magma melt. Thisbody is responsible for Yellowstone’s youthfulvolcanic history and its expanse of 10,000geysers, hot springs, and fumaroles. Modeling ofglobally produced earthquake waves passingbeneath Yellowstone revealed an upper-mantle P-wave low-velocity body of partial magma meltextending from 80 to 250 km directly beneathYellowstone, but tilting 60° west up to 660 kmdeep, at the bottom of the mantle transition zoneand 150 west of Yellowstone – this body isknown as the Yellowstone plume.Contemporary deformation of Yellowstone isdominated by southwest-directed horizontalcrustal extension across the Yellowstone Plateauof up to 3 mm/yr, which is about one third of thetotal regional rate of extension. However, muchhigher rates of uplift and subsidence due tovolcanic processes occur at decadal scalesaveraging about 2 cm/yr. Unprecedentedaccelerated uplift (up to 7 cm/yr) has occurredsince 2004, which was modeled as magmaticrecharge of the Yellowstone magma chamber atdepths of 7-10 km.Tectonic stretching of the crust along withvolcanically related stresses are responsible forYellowstone’s earthquakes that represent one ofthe highest rates of seismicity in the WesternUnited States; recorded seismicity averages1,000 to 3,000 shallow earthquakes per year ofmagnitude 6 or less. There have been more than

32,000 well-recorded earthquakes inYellowstone from 1973 to 2009. Earthquakesthat are closely spaced in time and area aretermed swarms and are the common mode ofseismic energy release in the Yellowstonecaldera. From 1984 to 2006 there were morethan 69 swarms recorded in Yellowstone. Thelargest swarm was in late 1985 and occurred onthe northwest side of the caldera withaccompanying earthquakes as large as M4. Thisswarm revealed a 15-km northwestwardmigration of seismicity over three months,which was modeled as lateral migration ofhydrothermal fluids out of the caldera. The 1985swarm also signaled the cessation of calderauplift and subsequent reversal to calderasubsidence. The 2008-2009 Yellowstone Lakeswarm described here, is the largest in the lastdecade. Yellowstone is a seismically active areawith earthquakes associated with theYellowstone hotspot and migration of magma aswell as earthquakes along major normal faultswith evidence supporting a history of recurrentlarge-magnitude earthquakes.

see the following websites for more informationhttp://volcanoes.usgs.gov/yvo/http://www.seis.utah.edu/http://earthquake.usgs.gov/regional/qfaultsIn the United States, seismic hazard is expressed

as peak ground acceleration (PGA) on firmrock, in %g, expected to be exceeded in a 50-yrperiod with a probability of 2 percent. Data fromthe National Seismic Hazard Map, 2008.

Tectonic Setting and Swarm History2008-2009 Swarm

M < 33 - 4

Earthquake MagnitudeM < 44- 4.95 - 5.9> 6Caldera BoundarySwarm Locations 1984-2009

Quaternary Faults<150 years<10,000<130,000<750,000Class B

0 100Km

SCALE

REFERENCESStover, C.W., and Coffman, J.L., 1993, Seismicityof the United States: 1568-1989 (Revised), USGS Professional Paper 1527USGS, 2006, Quaternary fault and fold database for the United States, from USGS web site: http//earthquake.usgs.gov/regional/qfaults/Puskas, C. and R. B. Smith, 2009, Intraplate defor-mation and microplate tectonics of the of the Yellowstone hotspot and surrounding western U.S. Interior, J. Geophy. Res., accepted, 2009White, B.J.P., R.B. Smith, S. Husen, J. Farrell and I. Wong, 2009, Seismicity and earthquake hazard analysis of the Teton-Yellowstone region, Wyoming, J. Vol. Geotherm. Res, accepted, 2009.

1:250,000Scale

Yellowstone Lake Swarm December 2008 --January 2009 44.55° N., 110.3° W.Depth 0-10 kmM 0 --3.9 (UUSS)Over 1000 earthquakes have been located as part of this earthquake swarm. Eighteen events have been recorded in the range M3-4. Visitors and employees at the Yellowstone National Park reported feeling these earthquakes.

Peak Ground Accleration in %g (2% probability of exceedance in 50 years)

2 4 6 8 10 12 14 16 18 20 30 40 50 60 80 120 160

Epicentral RegionSwarms (various colors)

Year indicatedEarthquakes UUSS

M < 33 - 3.94 - 4.95 - 5.9> 6

Quaternary Faults<150 years<10,000<130,000<750,000 Class B (age unspecified)Volcanic VentsCaldera BoundaryResurgent Dome

ACKNOWLEDGEMENTSAnalysis done by the Seismology and ActiveTectonics Group, Department of Geology andGeophysics, University of Utah; data acquisitionand distribution done by the University of UtahSeismograph Stations, Salt Lake City, UT.Map prepared by U.S. Geological SurveyNational Earthquake Information CenterJanuary 2009Not approved for release by Director USGShttp://earthquake.usgs.gov/

1:1,000,000

Plot of depth versus location of the Yellowstone Lake swarm from south to north(south on left, north on right). Earthquakes are shown from Dec. 27, 2008 to Jan.8, 2009. The M3.0 and greater earthquakes are shown as stars, the smallerearthquakes are shown as circles. From University of Utah Yellowstone ResearchGroup.

Figure from University of Utah Yellowstone Research Group

Projection Albers Equal Area, Central Meridian 111°W

Mechanism for M3.9 eventon 28 December 2008

Yellowstone in winter, David Carver, USGS