An Unexplored Realm in the Heartland of the Southern Gulf ... - Famsi

Magnetic Data Analysis
For the purposes of this survey, a magnetic anomaly is an observed irregularity or
deviation from the normal total magnetic field strength at a location as measured by a
magnetometer. A positive anomaly is where the field strength is stronger than expected, a
negative anomaly occurs where the field strength is less than expected (Marshak
2001:67). Variations in the intensity of magnetic fields registered by a magnetometer are
measured in nanoTeslas (nT). At El Marquesillo, the Earth’s total field intensity based on
the International Geomagnetic Reference Field (National Geophysical Data Center 2005),
is 40921.6 nT. The measured intensity of the magnetic field varied about this value,
ranging from a low of 40800 nT to a high of 41040 nT, or a peak to peak amplitude of
240 nT. Numerous and varied positive and negative anomalies were detected by the
survey and classified into basic types.
Two notable anomalies are linear in nature and of varying length and amplitude.
Structure 109 contains a ramp-like appendage that runs to the east-northeast of the
structure. At the end of this ramp is Linear Anomaly 1, a 100 nT amplitude magnetic
anomaly that extends straight for approximately 120 m. This anomaly is not randomly
oriented, but is highly coherent. In Figure 4.23 the magnetometer data have been laid
over a topographic base map. This image illustrates that Linear Anomaly 1 is aligned
with the surface features, and if the direction of the anomaly is extended it intersects
Structure 84 and the large anomaly buried below it. Other magnetic anomalies parallel
Linear Anomaly 1 but have lower amplitudes and are shorter in map length.
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