Faultline Mapping and Urban Development of Cache Valley

Ryan Brunson, Takahisa Ota


Remote Sensing 576 Final Report


INTRODUCTION

The introduction of the Landsat satellite has allowed scientists and geologists to use accurate images of the earth's surface to identify geological features such as faults, fracture zones, earthquake zones, and to determine potential destruction from earthquakes. City and county planners are also using satellite images to help plan and track urban development through out the state. Our project was to use both of these desiplines to a) by using the Thermatic Mapper and other ancillary data digitize a faultline and earthquake zone in Cache valley and b) with the SPOT satellite images and arial photographs to track the urban development around this earthquake zone.

STUDY AREA

The area of study is located in Cache valley, Utah, which is approximatily 50 km long from north to south and 16 km wide from east to west. The valley is defined by the Wasatch mountains on the east and south, and the Wellsville mountains on the west. The area of focus is from Smithfield in the north to Paradise in the south along the "Logan" front. The study area is not heavily populated, a large portion of the valley being agricultural farms. Logan is the largest city with a population of approximatly 40,000. The valley is mostly flat with gradually sloping benches of anticlines, synclines and monoclines which leads to abrupt mountain slopes. The Logan and Bear rivers are the main rivers through the study area.

METHODS

The first information we gathered was u.s. geological survey maps of Cache valley. These maps showed the location of the fault lines and the locations of the earthquakes that have occured in the valley. The fault line, which is a strike-slip, starts from the north and follows closely to the base of the Wasatch mountatins on the west side of the valley down to Avon. The fault has a major split in the Hyde Park area. A branch extends from Hyde Park in a north east direction through the mountains. The "main" fault line can be divided into two sections. The first section extends from Richmond in the north down to Hyde Park and from the Blacksmith fork to Avon in the south. This section of the fault is the older portion. It dates back to the Pleistocene and suspected Quaternary age approximatly 10,000 to 1.6 million years old. The second section of the fault extends from North Logan to the Blacksmith fork. This is the younger section dating from the Holocene and late Pleistocene period approximatly 0-30,000 years old. The map also desplays selected epicenters and the magnitude of earthquakes that have occured from the years 1884-1974 (lighter circles) and 1975-1989 (darker circles). The larger the circle the greater the magnitude. Most geologists believe the fault will only be able to generate an earthquake around a 5.0 in magnitude.

Figure 1
1990 U.S.G.S. map 1:500,000


The main fault line is actually not one straight fault through the valley. The Logan fault is actually very broken and has a lot of very small branches. Most of which run from west to east off the main fault. Using the Cache valley Thematic Mapper image we used the AOI tools to digitized the fault line from Smithfield to Paridise. A subset was made of the AOI and using the Search and Mask commands a buffer zone was made around the faultline. This zone is approximatly 1000 ft. on both sides of the faultline. The buffer zone is needed for the fact that the exact location of the faultline is not known in every place of the valley, the fault is very broken, and this is the method most planners use.

Figure 2


Using the TM image of Cache valley with the faultline buffer zone we search and masked the buffer zone area again to make a subset showing just the buffer zone area of cache valley. Using this image we can see some of the areas that are developed in the buffer zone. The areas that are easily visable in the fault zone are first dam, the Logan golf and country club, the urbanized developments just north of the golf club, and the developed area just south of first dam.

figure 3


URBAN DEVELOPMENT

The urban development around and on the faultline has increased especially in the late 1980's and early 90's. In the Richmond development has occured right on the faultline. The faultline runs through the south east corner of the town. Smithfield has also developed up towards the fault line with the Smithfield golf course right on the fault line. Development twords Long hill and Bald hill are also in the zone with other new developments. Hyde Park, North Logan, and Logan areas past 1600 East are close to and have developments in the buffer zone. The Logan golf and country club along with First dam is also located on the fault. The areas south of Logan that has been developed in the zone include parts of River Heights, Blacksmith fork canyon area, Paradise, and Avon. An example of the urban development in part of the fault zone is Cliffside. In a 1977 ariel photo of Logan compared to the 1993 Spot image, we can see some of the growth that has occured in the area.

figure 4

1977 Logan city photo.

Figure 5

The Potential for new growth along the fault line is still possible. Each individual city makes it's own zoning ordinances. Many of these cities, such as Smithfield, have plans for new development in the faultline zone. According to Mark Teuscher of the county planning office, the main limits to developing the areas along the fault line are 1) the availibility of water 2) the slope of the land and 3) most of the area ia still used for agriculture. Most geologists believe that the Logan fault is only capable of producing a earthquake of a 5.0 so the risk of development on the fault is not that great compared to areas such as Salt Lake City.


CONCLUSION

Through the use of remote sensing, geological features such as earthquake faults, folds, and zones can be easily identified and maped. Remote sensing makes use of spectral light that brings out features that otherwise would not be noticable on the ground. We have use the Thematic Mapper and AOI tools to map a faultline zone through Cache valley. The use of the SPOT satellite images, aerial photographs, and on site observations allowed accurate classification of the developed urban areas in the faultline zone. The results showed that the most heavily urbanized area in the faultline zone is the southeast corner of Smithfield, eastern Hyde Park and North Logan, First dam, eastern Cliffside and eastern Hyrum. These are also the areas that have the most potential for future development.

Kobe earthquake