Preliminary Results, Helicopter Electromagnetic and Magnetic Survey of the Seco Creek Area, Medina and Uvalde Counties, Texas Bruce D Smith, Richard Irvine, Charles D. Blome, Allan Clark, and David V Smith

Index map

Geologic studies

Preliminary geologic map from Kyle and Collins HEM SURVEY RECHARGE ZONE RECHARGE ZONE CATCHMENT AREA CATCHMENT AREA CONFINED ZONE NOT CONFINED ZONE

Hydrology 101

Seco Helicopter 2002 HEM Survey SENSOR SYSTEM  6 EM Frequencies 400 – 100,000 Hz  Internal Magnetometer  High Resolution GPS  Laser Altimeter

Geology with flight lines Geologic Map Showing Flight Lines 81 square miles 200 meter line spacing Red dot – sink hole Black USGS funding Red EAA funding

100kHz Apparent Resistivity

25kHz Apparent Resistivity

6200Hz Apparent Resistivity

1500Hz Apparent Resistivity

400 Hz Apparent Resistivity

Depth section calculations UBC EM1DFM EMFLOW Differential Depth

Line Vertical Exaggeration ~x m 1 Mile 100m100m Trinity Group SinkholeSinkhole Del Rio Clay Edwards Group nothing SOUTH NORTH Geophysical structure correlation Mapped structure correlation SinkholeSinkhole

Geology with flight lines Geologic Map Showing Flight Lines 81 square miles 200 meter line spacing Red dot – sink hole Black USGS funding Red EAA funding

Line Resistivity depth section Vertical Exaggeration ~x m 1 Mile 200m200m Geophysical structure correlation Mapped structure correlation

STRUCTURAL MAPPING

STRATIGRAPHIC MAPPING

Final Pictures Project Funding Edwards Aquifer Authority: additional flying (50% increase) San Antonio Water System: electrical depth sections USGS: Geologic Discipline Water Resources Discipline

Line location