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Group 2 – FARM | Poster Abstracts
hidden by plow zone. For this reason is important appeal to geophysical studies for the location of
these geological features. In this study, two 100 MHz Ground Penetrating Radar (GPR) profiles
were carried out for comparison, first, with a trench log and, second, with a radon concentration
profile. For locate the study site we turn to a previous study carried out by Andrew Peter Thomas
in 1965. The first GPR profile was carried out near the trench reported by Thomas and serve us to
calibrate the GPR image. Afterward the radon (222Rn) concentration was measured in 9 stations
along a traverse profile to the Imperial Fault in the Colonia Castro of Mexicali, Baja California, with
the purpose of locate additional traces of the Imperial fault with the support of the second GPR
profile. The Radon results allow us to identify three stations where the values exceed 40 picocuries
per liter (pCi/L), these stations can be associated to fault traces, and two places where the peak
values are at the level of 20 (pCi/L). Although the station 5 are not a peak, the observed value of
13.80 (pCi/L) allow us to explain the results of second GPR profile. The average of the detected
radon concentration, that was of the order of 22.11 (pCi/L), is considered high in relation to those
measured for studies of effects in the health in a indoor radon study in the city of Mexicali. The
results of this study allow us to think in the possibility that exist places in Mexicali city and their
valley that have the same values or perhaps higher, mainly near areas to the geologic faults and
specially near to the Imperial Fault. Due to the apparent goodness of this study and to the lack of
outdoor radon studies we will continue with this kind of surveys in Mexicali city and its valley.
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SPECTRAL ANALYSIS OF THE SURFACE SLIP PROFILES AND SLIP INVERSIONS
FOR THE 2001 KOKOXILI (TIBET) EARTHQUAKE Lavallee D
The 2001 Kokoxili (Tibet) earthquake provides a unique opportunity to study surface slip profiles.
The surface slip profiles have been measured along the fault for a distance of the order of 270 km
without any significant change in the strike direction. Measurements include the displacement
parallel and perpendicular to the fault, however, the recorded earthquake slip profiles are
irregularly sampled. Traditional algorithms used to compute the discrete Fourier transform are
developed for data sampled at regular spaced intervals. It should be noted that interpolating the
slip profile over a regular grid is not appropriate when investigating the spectrum functional
behavior or when computing the discrete Fourier transform. Interpolation introduces bias in the
estimation of the Fourier transform that adds artificial correlation to the original data. To avoid this
problem, we developed an algorithm to compute the Fourier transform of irregularly sampled
data. It consists essentially in determining the coefficients that best fit the data to the Sine and
Cosine functions at a given wave number.
The algorithm is tested by computing the power spectrum of the slip profiles of the Kokoxili
earthquakes. In addition, we also compute the power spectrum for the slip inversions computed
for the Kokoxili earthquakes. For all the slip models, we found that the power spectrum curves are
attenuated according to a power law behavior. However the power laws characterizing the slip
inversions decrease at a faster pace when compared to the power law computed for the slip profiles
recorded at the surface. This result suggests that the correlation embedded in the slip models is
larger than the correlation computed for the slip profile recorded at the surface.
A similar comparison between the slip profile recorded at the surface on the Arifiye segment of the
North Anatolian Fault zone and a kinematic source inversion for the 1999 Izmit (Turkey)
earthquake lead to a similar conclusion.
2008 SCEC Annual Meeting | 195