T-1842 AN ACTIVE SEISMIC RECONNAISSANCE SURVEY OF THE MOUNT PRINCETON AREA CHAFFEE COUNTY, COLORADO by James Scott Crompton ProQuest Number: 10782043 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10782043 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 T-1842 A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the require­ ments for the degree of Master of Science in Geophysics. Signed: ■i/s * u>./ ames Scott Crompton Golden, Colorado Dat e: Y , 1976 Approved: Phillip R. Romig, Jr. Thesis Advisor George V. Keller Head of Department Golden, Colorado Date: # 1976 T-1842 ABSTRACT An active seismic-reconnaissance survey was conducted of the Mount. Princeton area, near Buena Vista, Colorado in the fall of 1975. The survey was designed to monitor large mining blasts from nearby mining operations at Climax and Monarch Pass, Colorado and Questa, New Mexico and to interpret these observations using refraction tech­ niques . The results indicate the importance of examining apparent azi­ muths of energy paths into a local array and comparing these azimuths with the known source-receiver geometry. Conclusions from this sur­ vey suggest the existence of lateral refractions from boundary features of the upper Arkansas Valley graben, correlating with the extension of the Rio Grande Rift as far north as Leadville, and a fast time residual due to a probable normal fault in the subsurface of Chalk Creek, south of Mount Princeton. This survey demonstrates that a modified version of the crustal refraction technique can be a very cost-effective means of surveying the velocity and structural character of a large project area. ii T-1842 TABLE OF CONTENTS Page A bstract..................................................................................................... ii List of Figures and Tables ................................................................. iv Introduction .............................................................................................. 1 Acknowledgments ................................................................................. 3 Regional Geologic Setting................................................................. 4 Geologic History.................................................................................... 8 Scope of Investigation and Operations ....................................... 11 Equipment ................................................................................................. 17 Observations ........................................................................................... 24 Interpretation .......................................................................................... 41 Evaluation of Active Seismic Technique .................................... 52 C o n clu sio n s........................................................................................... 56 Recommendations ................................................................................. 57 Bibliography..................................' ...............\........................................ 58 iii T-1842 LIST OF FIGURES AND TABLES FIGURES Page 1 Location M ap ........................................................................... 5 2 Geologic Cross S e c tio n..................................................... 7 3 Station Location M ap . 15 4 Schematic Diagram of Equipment..................................... 17 5 Frequency Characteristics .................................................. 19 6 WWVB Code .............................................................................. 20 7 Teleseism USSR 294-1232 .................................................. 22 8 Local Event 294-2051 ........................................................ 22 9 Climax Event 295-2113 ........................................................ 23 10 Refraction Profile Teleseism U S S R .............................. 28 11 Refraction Profile Teleseism Kuril Is * ............ 2 8 12 Refraction Profile Teleseism M exico ............... 29 13 Refraction Profile Elkhead M tn s ..................................... 31 14 Refraction Profiles Regional WNW ................................. 3 2 15 Refraction Profile Climax Refracted Azimuth .... 34 16 Refraction Profile Climax Geographic Azimuth. 35 17 Refraction Profile Monarch P a ss ......................... 3 7 18 Amplitude versus Distance curve ..................... 39 19 Three Station Apparent Velocity Vector ....................... 45 20 Lateral Refractions, Buena Vista .................................... 46 21 Arrival Time Residual D a t a .............................................. 49 2 2 Velocity and Structure M odels ....................................... 49 iv T-1842 TABLES Page 1 Station Coordinates . ..................................................... 16 2 Recorded E v e n ts ..................................................................... 25 3 Local Events .............................................................................. 40 v T-1842 1 INTRODUCTION The seismic refraction technique has been used for many years to obtain subsurface velocity and structure information. This tech­ nique was exploited extensively in the 1960's as part of the VELA Uniform program of crustal studies in the western United States and in the design of the large aperture seismic array (LASA) in eastern Montana. With the availability of nuclear test explosions and large mining blasts, large areas were surveyed using equipment designed specifically for this purpose (Warrick et al, 1961; Jackson and Pakiser, 1965; Pakiser, 1963; Jackson, Stewart and Pakiser, 1963; Capon, 1974). Because many different geophysical and geologic measurements can be made, exploration decisions must be made based on the strengths and weaknesses of each technique. The very real limitations of eco­ nomics, available equipment and time restrict these decisions even further. Survey methods which can investigate a large prospect area and delineate local features for further study provide an acceptable compromise between the conflicting demands of data acquisition and cost. One such survey method, the active seismic reconnaissance technique, is discussed in this thesis. MOUNT PRINCETON SURVEY Between October 20th and October 24th, 1975 , an active seismic reconnaissance survey was conducted of the Mount Princeton area, near Buena Vista, Colorado. This project was designed as a field T-1842 2 experiment to test a modified version of the crustal refraction program used in the VELA Uniform studies by recording mining shots from sev­ eral locations and interpreting arrival times as a refraction profile. The independent operations of the microearthquake equipment used allowed 24-hour continuous monitoring and good areal coverage over a large project area. Real time interpretation of data allowed for re­ location of stations away from problem locations thus improving the data quality in the field. The following is a list of the conclusions from this study: 1) The active seismic reconnaissance technique succeeded in surveying the large Mount Princeton project area by delineating the regional structure and by singling out specific local targets for further investigation. 2) Interpretation of apparent-azimuth data from several sources indicates that lateral refractions occur from both the east and west side of the upper Arkansas River Valley. 3) Within the project area, a fast time residual exists, due to a probable normal fault in the subsurface, corresponding to the Chalk Creek drainage feature. T-1842 3 ACKNOWLE DGE ME NTS I thank the members of my committee, Dr. David Butler, Dr. Eric Engdall, and Dr. F. Richard Yeatts, and especially my advisor, Dr. Phillip Romig for their help and support. This research was made possible through a contract between AMAX Exploration and MicroGeo- physics Corporation to conduct the active seismic experiment at Mount Princeton. I also appreciate the use of equipment, funding and val­ uable advice from Art Lange, AMAX Exploration and Dr. Butler and Paul Larry Brown of MGC. Special thanks to Ed Torrgeson of AMAX Exploration and Cal Brown at the Climax mine, who were most re­ sponsive to requests for information concerning times of blasting at Climax and Questa, New Mexico. C ; T-1842 4 REGIONAL GEOLOGIC SETTING The Mount Princeton prospect area is located in south-central Colorado, approximately 150 km southwest of Golden (see figure X, location map). Topographically, the area lies on the border of the Sawatch Range and the upper Arkansas River Valley, between Buena Vista and Salida in Chaffee County. The upper Arkansas River Valley, extending north from Salida to Leadville, is believed to be a continuation of the Rio Grande Rift Zone (Knepper, 19 74). The rift feature, which can be traced from northern Mexico through central New Mexico into central Colorado, approximately 960 km, has formed since mid-Tertiary time by the relative westward