We use data from a series of small (three to five stations) overlapping magnetovariational (MV) arrays to image variations of vertically integrated electrical conductivity in the crust of southwestern Washington. Two principal structures are revealed: a large north-south trending anomaly (the southern Washington Cascades Conductor (SWCC), which has been detected...
In a companion paper (Egbert et al., this issue) we describe the estimation of very long period (0.16 < T < 91 days) magnetotelluric (MT) impedances from 11 years of data collected at the Tucson geomagnetic observatory. Here we discuss the implications of these data for mantle conductivity. Using minimum...
Although there is increasing evidence that fluids may play a significant
role in the earthquake rupture process, direct observation of fluids in active fault
zones remains difficult. Since the presence of an electrically conducting fluid, such
as saline pore water, strongly influences the overall conductivity of crustal rocks,
electrical and...
Eleven years (1932-1942) of electric potential and magnetic measurement at the Tucson observatory
represent a unique very long period magnetotelluric (MT) data set. We report here on a careful reanalysis of this
data using modern processing techniques. We have developed and used novel methods for separating out the
quasi-periodic daily...
Long-period global-scale electromagnetic induction studies of deep Earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure. We describe approaches to inverting for both the external sources and three-dimensional (3-D) conductivity variations and apply these methods to long-period (T≥1.2 days) geomagnetic observatory...
A magnetotelluric (MT)transect has been obtained near latitude 45øN from the active Juan de Fuca
Spreading center, across the subduction zone and Cascades volcanic arc, and into the back arc Deschutes
Basin region. This paper presents the MT data set and describes its major characteristics as they pertain to
the...
Worldwide measurements of nearly 130C3 species covering all
major plant functional types are analysed in conjunction with
model simulations to determine the effects of mesophyll
conductance (gm) on photosynthetic parameters and their
relationships estimated from A/Ci curves. We find that an
assumption of infinite gm results in up to 75%...
Spectral analysis of the time-varying horizontal magnetic and electric field components yields the magnetotelluric (MT) impedance tensor. This frequency dependent 2x2 complex tensor can be examined for details which axe diagnostic of the electrical conductivity distribution in the Earth within the relevant (frequency dependent) inductive scale length of the surface...
Magnetotelluric exploration has been used to image along strike variations in the electrical resistivity structure of the San Andreas Fault at Parkfield, California. A low resistivity wedge extending to a depth of several kilometers is continuous over a horizontal distance of 8 km. The base of the wedge is coincident...
Electric and magnetic fields in the (10−4–1.0) Hz band were monitored at two sites
adjacent to the San Andreas Fault near Parkfield and Hollister, California, from 1995 to
2007. A data window (2002–2005), enclosing the 28 September 2004 M6 Parkfield
earthquake, was analyzed to determine if anomalous electric or magnetic...