G42A-01 INVITED
Afterslip and Aftershocks
Afterslip following a mainshock is found in a variety of frictional sliding regimes, including unstable sliding (B>A
in the rate and state friction formalism) as well as stable sliding (B G42A-02 INVITED
Surface deformation during the subduction zone earthquake cycle in southern Peru and northern Chile
We use InSAR, GPS, teleseismic, and strong motion data to constrain
the location of inter-seismic, co-seismic, and post-seismic fault slip
on the shallow megathrust in the southern Peru and northern Chile
subduction zone during the last 20 years. For six of the earthquakes
studied (6.7 < Mw < 8.4), we invert seismic and geodetic data both
jointly and separately to determine the rupture processes (co-seismic
deformation). In northern Chile, because of the spatially and
temporally dense geodetic data, we can clearly separate co-seismic and
post-seismic deformation. We document a complex mosaic of phenomena
including large earthquakes, post-seismic after-slip with a spatial
distribution that appears to be related to variations in coastal
morphology, and a completely aseismic pulse that may have triggered a
Mw 7.1 earthquake in 1998. In contrast to simple models of fault slip
behavior, this spatial heterogeneity indicates that frictional
parameters on the fault do not have a systematic transition with depth
and also vary rapidly along-strike. Finally, we discuss our ability
to measure inter-seismic deformation given the various sources of
noise in the InSAR data, including: changes in the water vapor content
of the troposphere, perturbations in the ionosphere, and uncertainty
in the precise orbital positions of the satellites.
G42A-03 INVITED
Detection of postseismic relaxation from the 1999 Hector Mine earthquake in southern Basin and Range GPS time series
We present evidence for the detection of postseismic relaxation from the 1999 M 7.1 Hector Mine earthquake in
the non-linearity of time series from the southern BARGEN GPS network. It is important to understand and
quantify the transient contributions owing to earthquake cycle effects near the Yucca Mountain nuclear waste
repository because these data are used to estimate interseismic secular strain increase that could eventually be
released in earthquakes. Most sites from the 35 site continuous GPS network, in operation since 1999, lie over
200 km from the earthquake. However, some of these time series exhibit significant curvature and spatial
variation that is similar to the predictions of models of postseismic viscoelastic relaxation following the recent
Mojave Desert earthquakes.
Central in our analysis is our attempt to distinguish between the expected non-linear signal in the time-series
and the network-wide common-mode signals that can occur over similar times-scales as the postseismic signal.
We discuss various regional filtering approaches and show their impact on our ability to infer the postseismic
relaxation parameters. One such approach investigates time series cross-correlations, which can help
distinguish between network-wide common-mode and spatially coherent regional signals predicted by
geophysical models.
In order to place stronger constraints on the postseismic decay-time, and to better evaluate the significance and
correctness of the postseismic displacement field, we estimate a transient component in the time-series of a
large number of SCIGN and BARGEN sites. The use of near- and far-field data allows us to infer whether the
near- and far-field postseismic deformation signals are significant differently from each other and what that can
tell us about the underlying postseismic processes.
G42A-04 INVITED
Physics of the Earth outer core and inner core from VLBI
We used several existing and homemade nutation series derived from VLBI delays using different analysis
strategies. Residuals with respect to the MHB 2000 nutation model corrected from atmospheric effects have been
analyzed in order to retrieve Earth's interior parameters. The method is based on the transfer function expressing
the ratio between rigid and non rigid nutations. In particular we have examined the value of the FCN resonant
period and quality factor in terms of physics of the Earth's core and the accuracy with which the parameters can
be retrieved considering the current VLBI developments. We have also looked at the inner core parameters and
have determined the impact of VLBI uncertainties of the physics of the inner core, and in particular on the inner
core magnetic field.
G42A-05 INVITED
Earth's shape variations: Geodetic observations and Crust-Mantle-Core rotation modeling
The geodetically observed length variations of latitude circles of the Earth testify an asymmetry of shape variations
of the Northern and Southern Hemispheres. The circles are pulled together in the Northern Hemisphere with a
lesser degree than stretched in the Southern Hemisphere. Meanwhile it was also supported by the secular radial
motions of geodetic observations and the secular geocenter motion trend to the North Pole of the Earth. These
relative motions of the Earth shells lead to inverse changes of the Earth shape as formation of fluxes on the Earth
surface as well as the intensity of many natural processes in the opposite hemispheres. The secular
asymmetrical change of the Earth hemispheres is an important signal to the Earth's interior activities, e.g. relative
oscillations or deformations of the core and mantle induced by the forced core-mantle interaction. The main
consequence of the relative displacement is the changes of tension states of the mantle layers in opposite
hemispheres. The inertia moment with respect to the polar axis of the Earth is decreasing in the Northern
hemisphere, while increasing in the Southern hemisphere. Furthermore, due to the mantle deformation under a
gravitational action of the displaced core, the centre of the Earth's mass is tended to the northern pole with velocity
0.9+/-0.2 mm/yr. These secular differences or drifts result in secular redistribution of masses in the Earth
hemispheres, increasing in the Northern Hemisphere and decreasing in the Southern Hemisphere.
G42A-06 INVITED
Short-period Variations of the Earth Rotation Parameters Observed by Very Long Baseline Interferometry
High-frequency polar motion and universal time variations are obtained from Very Long Baseline Interferometry
(VLBI). The goal is to detect short-period and episodic events with signatures below the 100 microarcseconds
(7.5 microseconds) level. Ter-diurnal variations in the order of 40 microarcseconds in polar motion have been
reported during the VLBI campaign CONT02, from October 16 to 31, 2002. But, no geophysical explanation with
similar amplitudes was provided. To resolve this enigma, we re-processed the VLBI data obtained during the
CONT96, CONT02, and CONT05 campaigns using identical an the most recent reduction models. Two
independent software packages were used, OCCAM61E and CALC SOLVE, to assure robustness of the Earth
rotation parameters (ERP) estimated with semi-hourly resolution over the fortnightly data sets. The long
wavelength signal was removed by a smooth function from the final ERP. Jumps in the ERP values at session
boundaries were identified. A heuristic and Fourier frequency analysis shows no significant ter-diurnal periods. In
addition, this high-frequency analysis allows to detect incorrect daily ERP values in the International Earth
Rotation and reference Systems (IERS) C04 series.
G42A-07
Diurnal and Semidiurnal Signals in Polar Motion and UT1: Comparison of Space-geodetic Observations with Geophysical Models
Polar motion and UT1 contain physical signals within the diurnal and
semidiurnal frequency bands. The dominant part (< 1 milliarcsecond -- mas)
is due to the gravitationally forced ocean tides. There is also a small
variation (< 0.1 mas) due to the direct influence of the tidal gravitation
on the triaxial structure of the Earth. The remaining part (< 0.1 mas)
comprises the atmospheric and nontidal oceanic influences driven by the
daily cycle in the solar heating.
The observational evidence of diurnal and semidiurnal signals in polar
motion and UT1 concerns mostly the purely harmonic ocean tide signals which
are expressed by conventional models (IERS Conventions 2003). The
continuous observation campaigns, like CONT94, CONT02, CONT05, have been
also organized to estimate a less regular high frequency geophysical
signals in Earth rotation and compare them with models. Our recent work
(Bolotin and Brzezinski, 2006, Geophys. Res. Abstracts, Vol.8, EGU06-A-01665) demonstrated that it is also
possible to extract the diurnal and
semidiurnal signals in polar motion and UT1 extending over the last two
decades, from reanalysis of the archived VLBI observations. An important
independent estimation of such high-frequency signals in Earth rotation is
from the global circulation models with subdiurnal resolution of the
external geophysical fluids, the atmosphere and the oceans. Several
atmospheric angular momentum series with 4-times daily sampling have been
estimated on regular basis since 1992. Particularly important are the high-
resolution reanalysis data sets extending back to 1948. Also, several
subdaily time series of the nontidal oceanic angular momentum have been
produced recently.
This paper gives an overview of the recent advances in observation and
modeling of polar motion and UT1 at diurnal and subdiurnal periods. I will
focus attention on comparison between the estimates derived from the space-
geodetic measurements and those computed from the high-resolution
atmospheric and oceanic excitation data.
G42A-08
Toward a new strategy for multi-technique combined series of EOP and TRF
Since 2005 the Groupe de Recherche de Géodésie Spatiale (GRGS) provides on a routine basis series of
EOP and station coordinates from combined VLBI, GPS, SLR and DORIS geodetic techniques. The data
processing of these techniques is made with unique software: GINS and with the same standards which
guaranty homogeneity. Generated normal equations are then combined and solved with the DYNAMO software
package
The presentation will emphasized the way of processing, and particularly the strategy of merging common EOP
and TRF parameters. We will discuss as well the interest of combining tropospheric delay parameters for the
electromagnetic signals. Solutions are compared with those derived from International Services as well as from
IERS.
http:geodesy.unr.edu