Optimization of Tensor Controlled-Source Electromagnetic Exploration Methods: Case Study from Trachyte Mesa Intrusion, Henry Mountains, Utah

The Henry Mountains in Utah are home to several small igneous intrusions from the Late Oligocene to Early Miocene. One of the most critical small satellite bodies to the main intrusions of the Henry Mountains is the Trachyte Mesa intrusion. What is interesting about the Trachyte Mesa intrusion is that geologist and geophysicist are able to observe outcrops on the surface of Earth in order to characterize the mesa. An important question that is continuously being researched about this area concerns the emplacement of these intrusions. Scientist believe that by understanding the internal structure of these intrusions, answers regarding the emplacement of these intrusions will appear. There has been debate, however, regarding this internal structure. The main dispute is between two structural geologists who have competing ideas regarding Trachyte Mesa after conducting magnetic surveys in the area. Sven Morgan (2008) has concluded that the Trachyte Mesa intrusion internal structure is based on a sheet magma stacking model. Whereas Paul Wetmore (2009) believes that the mesa took the shape of the surrounding rock structures. In order to shed further light upon this dilemma, the original aim of the project was to conduct a tensor control-source electromagnetic characterization survey of the area and produce a model of the Trachyte Mesa intrusion. Due to several complications with responses from the equipment, the aim of the project was modified. The new goal is to discover the cause of the unusual signals from the equipment, whether it be from equipment malfunctions or the resistive environment present at Trachyte Mesa. With the extensive testing of equipment, a controlled-source electromagnetic survey process that will pave the way for future projects using the same methodology will also be established

Optimization of catheter’s implementation in the mold, in the case of vaginal HDR brachytherapy treatment

Background: The purpose of this study was to evaluate and compare results obtained in high dose rate (HDR) brachytherapy treatment of vaginal cancer. Different catheters distributions inside the custom mold were explored. The difference between those distributions is the position of the posterior catheter located near the rectum in the actual custom mold applicator used in different hospitals, each one having a catheter displacement of 0.5 which is equal to the length of a step position. The best catheters distribution offering an optimal dose distribution: better coverage of the clinical target volume (CTV), while reducing the dose received by organs at risk (OARs), were discussed. Materials and methods: A group of 60 patients treated with HDR brachytherapy, alone or in combination with external radiotherapy, was investigated. A custom mold is normally used for HDR brachytherapy vaginal cancer treatment. Three different geometrical positions of the catheters (G1, G2 and G3) and, consequently, 3 different dosimetries were simulated out for each patient on the CT images, using the Oncentra planning system. The coverage of the CTV was studied. Results: The average volume treated was 30.46 cc (min = 9.8 cc, max = 70.86 cc). The total prescribed dose, including external and internal radiotherapy, was 80 Gy. We evaluated conformity index (CI), dose homogeneity index (DHI) and conformality index (COIN) indices for the three implantation geometries to reach the same coverage criteria of the CTV. The D2cc parameter allowed the evaluation of the dose received by the OARs. For the rectum, a dose reduction of 9.67% (range 0.29–32.86) was obtained with the second geometry of implantation compared to 10.14% (range 1.43–28.33) with the third geometry. For the bladder, the second geometry of implantation showed a better preservation for this organ [15.93% (range 0.86–58.71) vs. 8.35% (range 0.33–30.43) with the third geometry]. The sigmoid was more protected using the second plan of implantation as well [6.33% (range 0.14–40.71) for the second implantation compared to 5.95% (range 0.33–36) for the third implantation]. Conclusions: G2 and G3 catheters’ distribution, having catheter position farther from the mold wall and so from the vaginal wall compared to the catheter position applied showed a better protection for the OARs while giving the same prescribed dose for the CTV

3D Imaging of Geothermal Faults from a Vertical DAS Fiber at Brady Hot Spring, NV USA

In March 2016, arguably the most ambitious 4D (3D space + over time) active-source seismic survey for geothermal exploration in the U.S. was acquired at Brady Natural Laboratory, outside Fernley, Nevada. The four-week experiment included 191 vibroseis source locations, and approximately 130 m of distributed acoustic sensing (DAS) in a vertical well, located at the southern end of the survey area. The imaging of the geothermal faults is done with reverse time migration of the DAS data for both P-P and P-S events in order to generate 3D models of reflectivity, which can identify subsurface fault locations. Three scenarios of receiver data are explored to investigate the reliability of the reflectivity models obtained: (1) Migration of synthetic P-P and P-S DAS data, (2) migration of the observed field DAS data and (3) migration of pure random noise to better assess the validity of our results. The comparisons of the 3D reflectivity models from these three scenarios confirm that sections of three known faults at Brady produce reflected energy observed by the DAS. Two faults that are imaged are ~1 km away from the DAS well; one of these faults (middle west-dipping) is well-constructed for over 400 m along the fault’s strike, and 300 m in depth. These results confirm that the DAS data, together with an imaging engine such as reverse time migration, can be used to position important geothermal features such as faults