Contemporary Vertical Motions Across the Sierra Nevada...
Transcript of Contemporary Vertical Motions Across the Sierra Nevada...
Contemporary Vertical Motions Across the Sierra Nevada/Great Basin Transition: GPS Measurements and ModelsW.C. Hammond, G. Blewitt, C. Kreemer, H.-P. Plag
[email protected] 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˚
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38˚
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−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