GLG 455/598 Advanced Field Geology

May 1 (afternoon), 2, 3 [Camping]

Typical evaluations of earthquake hazard are based upon establishing the geometry and activity of faults in an area. The geometry can be determined by mapping to establish potential rupture length and trace continuity (depth issues can be considered with seismicity, etc.--not for this class). Activity of faults refers to the slip rate and if possible slip per event. Quaternary lava flows are cut by normal faults near Wupatki, so we will map (using airphoto and topographic bases) the traces of a couple of faults and consider their activity by looking at the relationships to the lava flows and the degradation of the fault scarps. This area is in a zone of heightened seismicity (including several M6+ events this century) and earthquake hazard analysis for the Flagstaff region is timely.

Location: About 30 miles northeast of Flagstaff in the area of Hulls Canyon, Arrowhead Sink, and the Redhouse Basin adjacent to the northern portion of the Wupatki National Monument on the east side of Highway 89.

Mapping goals: Map the distribution of the different geologic units (including the lava flows and Quaternary units), establish their relative ages, map the traces of the normal faults in the region, and consider offset along the faults and the development of fault scarps on basalt and bedrock.

Mapping and notation strategy; Document the following:

1) Distribution of rock types. Where are the main units, what are they (describe them carefully and completely), and what did they look like when they were deposited or formed? How were they deposited or formed? What are the primary volcanic textures? Where was the vent? What is the relationship between the Mesozoic/Paleozoic units and the overlying rocks?

2) Soil descriptions. Can you use soils to determine relative ages of units or exposure ages of the scarps?

3) Relative ages of lave flows What are the relative ages of the lava flows? How do you know?

4) Landform development. What and where are the major landforms? How do the fault scarps vary with scarp height, age, and underlying rock type?.

5) Quality control and coverage. Be sure to quality control your observations. Try not to leave any gaps on the map. Make lots of careful observations reported clearly in your notebooks.

Questions to address in the write-up (Due May 12 by 5 PM to Arrowsmith)

(should be about 2-4 pages plus TWO figures [which will include a geologic map compiled to topographic base with a simple cross-section and a summary sketch describing your model of scarp development as a function of scarp height, underlying rock type and age]).

Writing is limited to less than 500 words for each section (1 and 2; 1A and 1B should be combined) Text should be space and-a-half. Note the included abstract as a sample of how to write these in the style of an abstract of your work.

1A) What is the geologic history of the mapping area? What are the relative ages of the units and the landforms?

1B) What is the map pattern of the fault traces? How do the offsets along them vary with position, offset marker (topography, flow base, bedrock)? What does the zone of faults look like in cross-section?

2) How do the fault scarps develop in this area? Starting with the figure from the McCalpin book by Wallace (Figure 31.12, page 105), how would you draw your own schematic figure that shows what a fault scarp looks like in consolidated materials like these? How does scarp development vary as a function of scarp height, underlying rock type and age?