Contemporary Vertical Motions Across the Sierra Nevada/Great Basin Transition: GPS Measurements and ModelsW.C. Hammond, G. Blewitt, C. Kreemer, H.-P. Plag

whammond@unr.eduNevada Geodetic Laboratory, Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory

University of Nevada, Reno

AbstractContemporary vertical motions of the Sierra Nevada are one key to under-standing longer term geologic processes that drive uplift, and are expected to at a rate on the order of 1 mm/yr. It has been demonstrated that verti-cal rates this small can be measured with GPS when station quality is high and the time series are long. (e.g. Bennett et al. 2009) We present vertical component GPS velocities for stations on the Sierra Nevada microplate (SNGV), Walker Lane and Basin and Range Province based on a recent complete reprocessing of all available GPS data with the latest version of the GIPSY/OASIS software and analysis models. Many stations of the EarthScope Plate Boundary Observatory nucleus (e.g. BARGEN and BARD) have recorded data for over 11 years, and have vertical rate uncertainties that are likely below 0.3 mm/yr. The Mobile Array of GPS for Nevada Transtension (MAGNET) complements these networks and has a greater geographic density of stations, but generally have time series that are shorter (6 years maximum). The variance of vertical velocities is a strong function of the length of the GPS time series, with large scatter for shorter time series. This suggests that we require at least 5 years of data on con-tinuous GPS sites in order to reliably infer rates of vertical motion of the crust when the rates are of this magnitude.

For stations with long enough time series, motions reflect at least two sepa-rate processes. The first is westward tilting of the SNGV microplate, with upward motion along its east side and downward motion in the central Great Valley of California. While the upward component is detected on several long-running stations on the west slope of the Sierra Nevada Moun-tains, the downward motions of stations in the Great Valley are effected in many locations by non-tectonic processes. The second process is postseis-mic relaxation from historic earthquakes in central Nevada and southern California. Adjusting the vertical GPS motions for postseismic effects using models of viscoelastic relaxation allows us to estimate long term vertical motions. We estimate the contemporary long term tilting rate of the SNGV from GPS velocities corrected for the effects of interseismic locking on block-bounding faults and viscoelastic postseismic relaxation.

Acknowledgements

Work on this project has been made possible by funding through the National Science Foundation’s EarthScope Program via project 0844389 “Revealing the Nature of Contemporary Uplift and Collapse in the Sierra Nevada - Great Basin System”.

Conclusions

• Many GPS stations in the Sierra Nevada/Great Basin transition have enough data (> 5 years time series) to provide reliable rates of vertical motion of the solid Earth from GPS.

• The number of such stations will increase dramatically in the next few years as the EarthScope Plate Boundary Observatory and MAGNET GPS stations continue to collect data.

• Early results show that GPS stations on the Sierra Nevada western slope tend to move upwards in an Earth center of mass (CM) reference frame, and stations in the Central Valley of California move downward. Rates in the east-ern NV Basin and Range are extremely similar (RMS ~0.2 mm/yr). Rates in the Walker Lane, where strain rates are highrer, are more variable.

• Results suggest a westward structural tilting rate that is bounded by 2 mm/yr east block uplift, 2 mm/yr west block subsidence, separated by ~100 km. This gives ~2 degrees/My upper bound for contemporary structural tilting of the block.

• Postseismic viscoelastic relaxation from 19th and 20th century earthquakes is most likely the cause for the pronounced ongoing ~2 mm/yr uplift in central Nevada.

• Postseismic relaxation from these earthquakes is likely not the cause of the vertical motions seen on the west slope of the Sierra Nevada.

References

Bennett, R. A., N. P. Fay, S. Hreinsdottir, C. Chase, and G. Zandt (2009), Increasing long-wavelength relief across the southeastern flank of the Sierra Nevada, California, Earth and Planetary Science Letters, 287, 1-2, 255-264.

Hammond, W. C., C. Kreemer, and G. Blewitt (2009), Geodetic constraints on contemporary deformation in the northern Walker Lane: 3, Postseismic relaxation in the Central Nevada Seismic Belt, in Late Cenozoic Structure and Evolution of the Great Basin – Sierra Nevada Transition, edited by J. S. Oldow and P. Cashman, pp. 33-54, Geological Society of America.

Pollitz, F. F. (1997), Gravitational-viscoelastic postseismic relaxation on a layered spherical Earth, Journal of Geophysical Research, 102, 17,921-917,941.

Above) Horizontal GPS velocities for stations in California and Nevada from MAGNET and other continuous GPS stations. Rates are with respect to stable North America. Sierra Nevada/Great Valley microplate moves northwest and has a decidedly counter-clockwise rotation, which contributes to variations in the pattern and style of deforma-tion in the Walker Lane. Red stations are MAGNET, blue are continuous sites.

Above) Station distribution showing MAGNET and continuous GPS sites in California and Nevada. Ultimately, the vertical GPS velocity field with have at least this geographic density when at least 5 years of data are collected at each sites. Color represents the length of the time series that are presently avail-able. Blue > 5 years, Red < 2 years.

Above) Vertical GPS velocity for stations with >5 years of data (see above left) and with annual oscillations less than 4 mm in amplitude. We remove stations with strong annual os-cillations because these bias the rates and because these sites tend to be located in places that are not stable bedrock. Labels are site names. The vertical component of these rates are in ITRF2005, and thus are in an Earth center of mass reference frame. Also areas strongly affected by non-tectonic processes are removed (e.g. Coso and Long Valley).

Right) Histograms of time series length for stations used in this analysis (left) versus all PBO, BARGEN and MAGNET sta-tions that are, or will be, available in the near future (right). This illustrates how many more reliable vertical rates will become available to study long term uplift and collapse of the Sierra Nevada/Great Basin system.

All GPS StationsGPS Stations with

Vertical Rates Shown Above

Time Series Length (years) Time Series Length (years)

N=

Above) Profile of GPS velocity in Earth center of mass refer-ence frame across a profile that extendes from the California Central Valley, across the Sierra Nevada, Walker Lane, central Nevada Seismic Belt and into the eastern Nevada Basin and Range. Rates in eastern Nevada are very similar, with RMS<0.3 mm/yr. Central Nevada Seismic Belt uplift of ~2 mm/yr is evi-dent. The signal is more complex inside the Walker Lane, where crustal strain rates are an order of magnitude larger than in the Basin and Range. Sierra Nevada uplift is on the order of 1-2 mm/yr as shown by site CMBB, at the far left.

Above) Vertical velocity predicted from a model of viscoelastic postseismic relaxation from earthquakes in of the central Nevada Seismic Belt. Model derived by Hammond et al., (2009) using VISCO1D code of Pollitz, (1997). Magneta bars show location and length of rupture for each earthquake in the model. Uplift of 2 mm/yr in central Nevada bears strong resemblance to observed vertical GPS velocity (above left).

Above) Vertical velocity interpolated from GPS rates obtained from time series with at least 5 years of data. Rates in the Basin and Range of eastern and southern Nevada are extremely simil-are, with RMS <0.3 mm/yr. Sites around the Central Nevada Seismic Belt move upward ~2 mm/yr, sites in Walker Lane show more complex patterns, but are generally more simliar to east-ern Nevada. Sierra Nevada stations with sufficient data are few, and limited to the western slope, but move generally upward by 1-2 mm/yr. Vertical rates in the Central Valley of California are more complex, probably owing to lack of sites on extremely stable bedrock.

mm

/yr

mm

/yr

Below Left) Same as above, except using 7 year minimum time series length. Below right) same except using 4 years minimum time series length. Trade-off between improved geographic resolution of vertical rate, and inclusion of higher variance (owing to noise) rates is evident.

Horizontal GPS Velocities in California and Nevada

−122˚ −120˚ −118˚ −116˚ −114˚

36˚

38˚

40˚

42˚

−122˚ −120˚ −118˚ −116˚ −114˚

36˚

38˚

40˚

42˚

Available GPS SitesPresent Length of GPS Time Series

Longitude

Latit

ude

< 3 years3 - 4 years4 - 5 years5 - 6 years> 6 years

Nevada

Oregon

UtahArizona

California

MAGNET GPSContinuous GPS

−126

˚

−124

˚

−122

˚

−120

˚

−118

˚−1

16˚

−114

˚−1

12˚

38˚

40˚

42˚

12 mm/yr

−122 −121 −120 −119 −118 −117 −116 −115 −11435

36

37

38

39

40

41

42

Longitude

Latit

ude

Pleasant Valley

Cedar Mountain

Rainbow/Stillwater

Fairview Peak

GKLBWBDixieValley

Owens Valley

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

−122 −121 −120 −119 −118 −117 −116 −115 −11435

36

37

38

39

40

41

42

Longitude

Latit

ude

Minimum 5 YearsTime Series Length

ALAM

ANTB

ANTE

APEXARGU

BAMO

BEAT

BEDE

BEPK

BKAP

BRAD

BUFF

BULLBUST

BVPP

CANDCARH

CCCC

CHLO

CHO1

CMBB

CMODCNDR

CPBN

CRAT

CRBT

DECHDIAB

DOYL

DYERECHO

EGAN

ELKO

FITTFLAN

GABB

GARL

GDECGOL2GOLD

GOLMGOSH

GR8V

HOGS

HONY

HUNTISLK

JERS

JNPR

JOHN

KYLE

LAND

LEWI

LIND

LITT

LNMT

LOWS

LUTZ

MASW

MCKIMCOY

MEE1MEE2

MERC

MHCB

MILL

MINE

MNMC

MODB

MONB

MONI

MOUN

MULL

MUSB

NEWS

P067

P072P127

P171

P210

P213P217P218

P229P230

P249

P256P266

P278P281P282P283

P284P287

P295

P298

P300

P301P302

P526P530P532P539P541

P591

P594

PALO

PERL

PKDB

PMTN

POIN

POMM

POTB RAIL

RAIN

RAMT

RDMO

REDR

RELA

RENO

REPO

ROGE

RUBY

RUSS

RYAN

S300

SAOB

SHIN

SHLD

SHOS

SKUL

SMYC

SODB

STRI

SUTB

TATE

TBLP

THCP

TIVA

TOIY

TONO

TUNG

UPSA

USLO

VIGUVIRC

VIRP

WATC

WGPP

WINV

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

Model of Postseismic Relaxation

−122˚ −120˚ −118˚ −116˚ −114˚

36˚

38˚

40˚

42˚

−122˚ −120˚ −118˚ −116˚ −114˚

36˚

38˚

40˚

42˚

ALAM

ANTBANTE

APEX

ARGU

BAMO

BEAT

BEDE

BEPK

BKAP

BRAD

BUFF

BULLBUST

BVPP

CANDCARH

CCCC

CHLO

CHO1

CMBB

CMOD

CNDR

CPBN

CRAT

CRBT

DECHDIAB

DOYL

DYERECH

EGAN

ELKO

FITTFLAN

GABB

GARL

GDEC

GOL2GOLD

GOLM GO

GR8V

HOGS

HONY

HUNT

ISLK

JERS

JNPR

JOHN

KYLE

LAND

LEWI

LIND

LITT

LNMT

LOWS

LUTZ

MASW

MCKI

MCOY

MEE1MEE2

MERC

MHCB

MILL

MINE

MNMC

MODB

MONB

MONI

MOUN

MULL

MUSB

NEWS

P067

P072P127

P171

P210

P213P217

P218

P229P230

P249

P256

P266

P278P281P282P283

P284P287

P295

P298

P300

P301P302

P526 P530P532P539P541

P591

P594

PALO

PERL

PKDB

PMTN

POIN

POMM

POTBRAIL

RAIN

RAMT

RDMO

REDR

RELA

RENO

REPO

ROGE

RUBY

RUSS

RYAN

S300

SAOB

SHIN

SHLD

SHOS

SKUL

SMYC

SODB

STRI

SUTB

TATE

TBLP

THCP

TIVA

TOIY

TONO

TUNG

UPSA

USLO

VIGUVIRC

VIRP

WATC

WGPP

WINV

Vertical Rate from GPS at Siteswith >5 years of data, and annual osciallations < 4mm

2 mm/yr down

2 mm/yr up

Longitude

Latit

ude

−122 −121 −120 −119 −118 −117 −116 −115 −11435

36

37

38

39

40

41

42

Longitude

Latit

ude

7 Years MinimumTime Series Length

ALAM

APEXARGU

BAMO

BEAT

BEPK

BKAP

BULLBUST

BVPP

CANDCARH

CCCC

CHLO

CHO1

CMBB

CPBN

CRAT

CRBT

DECHDIAB

DYERECHO

EGAN

ELKO

GABB

GARL

GDECGOL2GOLD

GOSH

HOGSHUNTISLK

JNPR

JOHN

LAND

LEWI

LIND

LITT

LNMT

LOWS

LUTZ

MASW

MEE1MEE2

MERC

MHCB

MINE

MNMC

MODB

MONB

MONI

MUSB

NEWS

PERL

PKDB

PMTN

POIN

POMM

RAIL

RAMT

RELAREPO

ROGE

RUBY

RYAN

S300

SAOB

SHIN

SHLD

SHOS

SKUL

SMYC

SODB

STRI

SUTB

TATE

TBLP

THCP

TIVA

TOIY

TONO

TUNG

UPSA

USLO

WATC

WGPP −2

−1.5

−1

−0.5

0

0.5

1

1.5

2

−122 −121 −120 −119 −118 −117 −116 −115 −11435

36

37

38

39

40

41

42

Longitude

Latit

ude

ALAM

ANTB

ANTE

APEXARGU

ARMY

ASHM

BAMO

BATM

BATT

BEAT

BEDE

BEPK

BKAP

BRAD

BUFF

BULLBUST

BVPP

CAMB

CANDCARH

CCCC

CHLO

CHO1CLAN

CMBB

CMODCNDR

COAL

COLD

CPBN

CRAMCRAT

CRBT

DECHDIAB

DOYL

DYERECHO

EGAN

ELKO

FITTFLAN

FLEM

GABB

GARL

GDECGOL2GOLD

GOLMGOSH

GR8V

HOGS

HONY

HUNT IBEX

INDI

ISLK

IXLC

JERS

JNPR

JOHN

JUNI KYLE

LAND

LAPL

LEWI

LICE

LIND

LITT

LNMT

LOWS

LUDW

LUTZ

LYAL

MASW

MCKIMCOY

MEE1MEE2

MERC

MHCB

MICH

MILL

MINE

MNMC

MODB

MONB

MONI

MOUN

MULL

MUSB

NEVA

NEWS

NOPE

NPAS

P067

P072P095

P127

P145

P171 P175

P210P212

P213P217P218

P227P228P229P230

P234P236P238P244

P247P249P251

P252

P255

P256P257

P266

P272

P273P274P275

P276

P278P280

P281P282P283P284

P285

P287P288P290P294

P295P297P298

P300

P301P302

P303

P305

P306

P309

P464

P467

P516P523

P526P529

P530P532P533

P536P537P538

P539P540P541

P543

P544P546P547

P563

P566

P567

P571

P579P591

P594P595

P611P615P617

P618

P621

P622P626

PALO

PERLPHIN

PINE

PKDB

PLEA

PMTN

POIN

POMM

POOS

POTB

QCY2

RAIL

RAIN

RAMT

RATTRDMO

REDR

RELA

RENO

REP2REP3REP4REPO

ROGE

RUBY

RUMP

RUSS

RYAN

S300

SAOB

SEVN

SHIN

SHLD

SHOS

SHSH

SKUL

SLI4

SMIT

SMYC

SODB

SPRK

STRI

SUTB

SWEE

TATE

TBLP

THCP

TIVA

TOIY

TONO

TRAC

TRINTUNG

UPSA

USLO

VIGUVIRC

VIRP

VONS

WALKWASS

WATC

WGPP

WILC

WINV

WOND

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

4 Years MinimumTime Series Length

ALAMANTB

ANTE

BAMO

BEAT

BEDE

BRAD

BUFF

BULLBUSTCHLO

CMBB

CRAT

ECHOEGANELKO

FITT

GOLM

GOSHJERS

KYLE

LEWI

LITT

MCKI

MCOY

MERC

MILL

MINE

MONI

MOUN

MULL

NEWS

P127PALO

PERL POIN RAI L

RAIN

RDMO

RELA

RENO REPORUBY

RUSS

SKULSTRI

TATE TIVA

TONO

TUNG

UPSAVIRC

VIRP

−120 −119 −118 −117 −116 −115 −114−1

−0.5

0

0.5

1

1.5

22.5

Longitude

Verti

cal G

PS V

eloc

ity

−121

Basin and RangeCentral Nevada Seismic BeltWalker LaneSierra Nevada

2 4 6 8 100

50

100

150

200

250

300

2 4 6 8 100

10

20

30

40

50

60