Controlled source audio-frequency magnetotellurics (CSAMT) data collection in the Grand Canyon West and Plain Tank areas of the western Hualapai Reservation, Arizona, August to November, 2017

Controlled source audio-frequency magnetotellurics (CSAMT) data were collected in the Grand Canyon West and Plain Tank Flat areas of the western Hualapai Reservation, Arizona, to better understand the hydrogeology of the area. CSAMT data provide vertical cross-section (profile) data about the resistivity of the subsurface, which may be related to lithologic boundaries and (or) grain-size distribution in the subsurface. CSAMT involves transmitting a current of electricity at various frequencies in one location, and measuring the magnetic response and electrical current between electrodes spaced along a receiver line several kilometers from the transmitter. Data were collected using a GGT-30 transmitter and GDP32-II receiver (Zonge international. Inc.). Data processing and inversions were carried out using Zonge International, Inc. software. As a processing step, measured resistivity values must be "inverted", or converted to 2-d vertical resitivity profiles. The inversion step involves identifying a subsurface resistivity model that best matches the data, while accounting for the measurement precision of the data.

The primary data format is a .kmz file that can be viewed in Google Earth or other geospatial browsers. The .kmz file can be unzipped to view the source images. Subsurface resistivity cross-sections are shown at their respective geographic locations, elevated above the land surface. The vertical scale for each cross-section is approximately identical. The .kmz file can be downloaded from this page.

In addition, raw data, station location data, and inversion data are provided. These files are useful for reprocessing the inversions and testing alternative inversion schemes. They can be downloaded from the child pages linked below.

Raw Data: Text files output by the data-collection instrument (GDP32-II, Zonge International, Inc.); averaged values are used in the inversion. These data may be useful for testing alternative inversion schemes.

Station Data: Text files with the receiver locations for each line. data were collected using a handheld GPS.

Inversion Data: Text files of inverted resistivity values, starting model values, and corresponding x, y, z coordinates These files allow the user to recreate the inversions provded in the accompanying kmz file.