By inverting EarthScope long-period magnetotelluric (MT) data from the southeastern United States (SEUS), we obtain electrical conductivity images that provides key insights into the geodynamics of this region. Significantly, we resolve a highly electrically resistive block that extends to mantle depths beneath the modern Piedmont and Coastal Plain physiographic provinces....
Magnetotelluric (MT) data from two sites 150 and
300 km southeast of San Francisco, California (geomagnetic
dipole latitude: 43 degrees, L approximately 1.9) show that
the usual MT assumption of spatially uniform external magnetic
fields is violated to a significant degree in the period
range 10-30 s. Inter-station transfer functions...
Full Text:
in Mid‐Latitude Geomagnetic Transfer Functions” by Gary D. Egbert, Markus Eisel, O
Magnetotelluric (MT) data from two sites 150 and
300 km southeast of San Francisco, California (geomagnetic
dipole latitude: 43 degrees, L approximately 1.9) show that
the usual MT assumption of spatially uniform external magnetic
fields is violated to a significant degree in the period
range 10-30 s. Inter-station transfer functions...
Full Text:
DC trains and Pc3s: Source effects in mid-latitude
geomagnetic transfer functions
Gary D. Egbert
We describe novel hybrid algorithms for inversion of electromagnetic geophysical data, combining the computational and storage efficiency of a conjugate gradient approach with an Occam scheme for regularization and step-length control. The basic algorithm is based on the observation that iterative solution of the symmetric (Gauss-Newton) normal equations with conjugate...
I derive probability densities for virtual geomagnetic pole( VGP) longitudes for a general statistical model of
local magnetic field variations. I show that even for very
simple statistically homogeneous models of secular variation,
the distribution of VGP longitudes is peaked 90° away
from the sampling longitude. Thus, when sites are...
The Juan de Fuca plate system is what remains of Farallon plate subducting under the continental North American plate. Blanco Transform Fault Zone (BTFZ) consists of a network of strike-slip faults discontinued by pull apart depressions which o↵sets the Juan de Fuca Ridge and the Gorda Ridge. Detailed analysis of...
Although satellite electromagnetic induction studies
have usually assumed a symmetric magnetospheric ring
current source, there is growing evidence for significant
source asymmetry. Here we apply empirical orthogonal
function methods to mid-latitude night-side hourly mean
geomagnetic observatory data to search for evidence of nonzonal
low-frequency source fields. The dominant spatial
mode...
We used data from Cascadia Initiative and Blanco Transform Fault Zone array of ocean bottom seismometers and hydrophone to look at the seismicity and specially depth of the Central Cascadia Continental Margin events. Events were detected and located automatically with Antelope software package (Boulder Real Time Technologies). We looked at...