Characterization of the Upper Arkansas River Basin, Chaffee County Colorado Colorado School of Mines, Boise State University, Imperial College London Geophysics Field Camp 2009 June 4, 2009 Abstract Students specializing in geophysical investigations participated in a summer field session organized through the Colorado School of Mines, Boise State University, and Imperial Col- lege London in order to apply knowledge gained in the classroom. The 2009 Summer field session took place in Chaffee County, Colorado from May 10th through the 22nd before returning to Golden, Colorado for processing until June 5th. For the fifth year, the students conducted geophysical surveys in the Poncha Springs and Mount Princeton Hot Springs area, where both near surface and deep geophysical techniques were used. The data collected builds on the geological understanding of the area, and there- fore an increased understanding of geothermal activity in Chaffee County. Just north of the Mount Princeton Hot Springs area the students conducted an inves- tigation using seismic, gravity, and magnetics in order to help identify the large structures and basin fill associated with the Rio Grande Rift. At the area known as Mount Princeton Hot Springs, near surface geophysics was conducted to help understand the faulting and fractures that act as a conduit for hydrothermal flow. The methods used included high fre- quency 3D seismic, magnetics, gravity, D.C. resistivity, and self potential. Throughout the Mount Princeton area, passive seismic, vertical seismic profiling, and well logging were also used to better understand the geology and activity of the region. Surveys were conducted in the Poncha Springs area as reconnaissance for future, more in depth, surveys. This data will give an initial understanding of surface manifestations and possible faulting associated with the Rio Grande Rift, the San Luis Valley, and the Upper Arkansas Basin. Methods used were D.C. resistivity, magnetics, electromagnetics, self po- tential, and gravity. Following a thirteen day period of data acquisition in Chaffee County, the students re- turned to the Colorado School of Mines in Golden, Colorado for an additional two weeks of data processing. They drew many conclusions and made interpretations from the data collected. In the Field of Pain the data suggest a 40 to 50 m thick unconsolidated layer overlying the fractured granitic basement. The DC profile shows a deep geothermal anomaly of low resistivity which correlates with a positive SP anomaly in the same region. In the Chalk Creek valley a shear zone extends from the north east to the south west, just south of the Chalk Cliffs. There appears to be an upward migration of the water through this shear zone which then flows along the porous sediments towards the south in this area. At Poncha Springs, the high conductivity zones in the EM data and the low resistivity in the DC profiles suggest hot water distribution in the subsurface. The magnetic data suggests that a fault near the Boy Scout camp which acts a a conduit to hot water. The deep seismic suggests that the depth to the basement is approximately 2000m. Also identified on the deep seismic are two major faults on the west end and two minors at the east end of the cross-section. An alteration zone is identified between the faults and a pos- sible Precambrian northeast trending shear zone. 2 Acknowledgements Our geophysics field camp could not have been possible without the support of many organizations and individuals. We greatly appreciate the generous financial contributions made by the Society of Exploration Geophysicists and the United States Department of Energy to this years field camp. In addition, Chaffee County not only let us use their roads for data collection, but also granted support which helped pay for our meals. We also want to thank those companies who donated not only funds but also knowledge and equipment, including CGG/Veritas and Sercel. CGG/Veritas lent vibroseis trucks along with personel. Rod Kellaway not only supervised the seismic operation, but provided a great deal of insight on their use. Sercel USA lent us Tom Chatham who guided us through the tangle of seismic data acquisition. For the formidable task of processing the deep seismic data, GX Technol- ogy (an ION Geophysical company) made software and equipment available. Hans Ecke, Sissy Theisen, Joe Zahrt, and Gerardo Garcia gave specific contributions in time. Landmark (Halliburton) provided a ProMAX license for the computer brought in the field. We would also like to thank the University of Texas (NEES) for letting us use their mini-vibroseis truck. Many individuals offered their valuable time and know-how to advance our understand- ing of the areas geology and hydrology. Fred Henderson supplied his experienced take on what is occurring geologically within the Valley and what they believe to be the hydrological situation. We are also grateful for the accommodations provided by Deer Valley Ranch and Mt. Princeton Hot Springs. Many local private citizens and organizations allowed access to their property. Bill Moore made his geothermal well available. Many others allowed us to plant flags and make mea- surements across or near their property. Many helped out by expressing enthusiasm for our project. We apologize if we left anyone off the following list of contributors. Jim Clark Joe Cogan Doug Troudt Steve Long Mr. and Mrs. Nicoles Becky Massey Tom Massey Ed Farrow Fred Berkman Seth Heins Frontier Ranch City of Salida City of Poncha Springs Many professors and staff members from Colorado School of Mines, Imperial College Lon- don and Boise State University contributed their valuable time and assisted us with our geo- physical investigations: Michael Batzle, Rich Krahenbuhl, Andre Revil, Helmut Jakubowicz, Spencer Wood, Kaspar van Wijk, and Lee Liberty. Robert Raynolds of the Denver Museum of Nature and Science offered his knowledge and experience of the geology of the entire Up- per Arkansas River Valley. Terry Young, Dawn Umpleby, and Michelle Szobody contributed to the organization and logistics of the trip for all the students. Graduate students Brianne Hamm, Alicia Hotovec, Grace Cairns, Andy Lamb, Thomas Blum and Dylan Mikesell as well as CSM graduates Jeff Godwin, Arianne Dean and Tyson Jesser worked along side with 1 the students ensuring that the surveys ran smoothly and efficiently. CSM Alumni, Evan Genaud spent many hours helping students with seismic processing. Also a big thanks to Brian Passerella, the field equipment coordinator, for his tireless efforts to keep equipment running. 2 Students Colorado School of Mines Boise State University Imperial College London Bo Beins Shannon Chollett Yernur Akashev Brandon Bush Sean McShane Akeem Akintayo Joey Cohrs Andrew Nies Nafa Al Jahdhani Sarah Devriese Randi Walters Ahmad Alghamamdi Yuanzhong Fan Horry Parker∗ Kate Chapman Farnoush Forghani Antonio Pereiray Anna Dawson Renee Francese Khushal Gohel Roxy Frary Hamizah Hj Hamzah Leslie Godfrey Nurbek Karatalov Joyce Hoopes Bakhytzhan Khairaliyev Gordon Johnson Christopher Leader Colin Leek Cristian Moncada Palacio David Manthei Tenice Nangoo Craig Markey Jeremy Soule Michael Mitchell Krystel-Maria St Clair Cliff Preston Christopher Swift Orion Sandoval Thomas Weight Jessie Shirey Victoria Wilson Kristen Swaim Ariel Thomas aHorry Parker attends University of Georgia bAntonio Pereira attends Texas A&M 3 Disclaimer The information contained in this document is derived from a summer field camp for undergraduate and graduate students in Geophysics at the Colorado School of Mines, Boise State University, and the Imperial College London. The primary purpose of this camp is to teach students the hands-on use of a wide variety of geophysical methods. Secondarily, this camp focused on the issues associated with aquifer recharge dynamics in the Upper Arkansas Valley. However, the processing and interpretation of data gathered in the basin was done, mostly on a first-time basis, by students inexperienced in these activities. There- fore, the results should be regarded appropriately. Neither the Department of Geophysics nor the Colorado School of Mines guarantees the validity of the information presented in this document. 4 Contents 1 Introduction 10 1.1 Background Information . 10 1.2 Objectives . 11 1.3 Survey Locations . 12 2 Geologic Background 16 2.1 Introduction . 16 2.2 Geology of the Upper Arkanasas Valley . 17 2.3 Stratigraphic Column . 22 3 Seismology 23 3.1 Introduction . 23 3.2 Wave Theory . 23 3.2.1 Reflection . 23 3.2.2 Refraction . 23 3.3 2D Deep Seismic . 25 3.3.1 Introduction . 25 3.3.2 How the Seismic Method Works . 25 3.3.3 Equipment . 26 3.3.4 Location and Survey Design . 27 3.3.5 Processing . 28 3.3.6 Interpretation . 37 3.3.7 Error Analysis . 45 3.3.8 Conclusions . 49 4 3-D Seismic 51 4.1 Introduction . 51 4.2 Acquisition Parameters . 52 4.3 Processing . 53 4.4 Interpretation . 60 4.5 Conclusions . 61 5 5 Vertical Seismic Profile 63 5.1 Introduction . 63 5.2 Survey Design . 64 5.3 Processing . 66 5.3.1 Frontier Ranch Zero Offset VSP . 66 5.3.2 Dead Horse Lake Zero Offset VSP . 67 5.3.3 Dead Horse Lake Radial VSP survey . 69 5.4 Error Analysis . 72 5.5 Interpretation . 73 5.5.1 Frontier Ranch . 73 5.5.2 Dead Horse Lake . 74 6 Electromagnetic 76 6.1 Introduction . 76 6.2 Istrumentation . 77 6.2.1 EM-31 . 77 6.2.2 EM-34 . 78 6.3 Data Reduction . 79 6.4 Data-Observations . 80 6.4.1 EM-31 . 80 6.4.2 EM-34 . 84 6.5 Conclusion . 87 7 Magnetics 88 7.1 Method . 88 7.2 Survey Design & Data Collection . 90 7.2.1 North Site { East West Deep Investigation Group . 91 7.2.2 North Site { Mr. Long`s Field . 91 7.2.3 South Site { Poncha Springs Boy Scout Camp .