Seismic and vibration hazard investigations of Chaco Culture National Historical Park

Abstract

The potential for damage to structures in Chaco Culture National Historical Park resulting from earthquakes, landslides, industrial blasting, road building and vehicular traffic has been investigated. The Historical Park, located in northwestern New Mexico, contains over 2,000 known archeological sites. The structures of interest, many of them multistory and a few containing over 200 rooms, date from the 11th and 12th centuries. Most of the remaining walls are 1.5 to 3.0 m in height, but a number exceed 5.0 m. A 2.0 mm/sec particle velocity is recommended as the upper limit for induced motions in the structures resulting from industrial blasting, road building and vehicular traffic. Minimum distances of these activities from the structures are recommended based on field recordings and analysis of the induced vibrations from these sources. Minimum distances of 1.2 km from blasting, 0.5 km from railroad traffic, 45 m from road building and 25 m from vehicular traffic are recommended based on normal blasting practices in the area, conventional rail traffic, usage of road building equipment and normal vehicular traffic patterns. Recommendations are also made for controlling vibrations from one road in the Historical Park considered to be too close to historical structures. Levels of expected ground motion from earthquakes, even for relatively short time periods of interest such as 50 yrs, indicate that possible future earthquake damage to the structures should be considered. The implication is that at least some of the past deterioration of the structures in the Historical Park may have been caused by earthquake ground motion.

Induced ground-vibration study at Pueblo Grande, Phoenix, Arizona

“…These frequencies and damping values are generally comparable to those found in the one-two story archeological structures (King andAlgermissen, 1985, King andothers, 1986). However, it is important to note that the wall vibrations due to the locally induced sources show that the walls tend to respond more selectively to the higher modes in the 11 to 35 Hz range.…”

“…Regression analysis of the data by an exponential curve fit gives the relationship of h=40.7e-0.13f. The equation is very similar to the one derived from the testing of Anasazi walls in Chaco Canyon (King and Algermissen, 1985). All tests except the roof tests are from the horizontal-short-axis of walls.…”

“…The roofs of the museum were similarly tested, except that a vertical motion-sensing seismometer was placed in the midpoint of the roof and shaking was induced by a person doing knee-bends or by a weight drop. This technique has been described in detail by Hudson and others (1964) and King (1969King ( , 1985. The peak frequency and harmonics of that frequency determined from the spectrum derived from the wall test data were considered to be the frequencies to which the walls were most sensitive.…”

Vibration investigation of the museum building at White Sands National Monument, New Mexico

“…5 J, L and T) are within the same general frequency range as the walls but, in general, have lower damping coefficients (Table 2). These frequencies and damping values are generally comparable to those found in one-to-two story structures Algermissen, 1985, King andothers, 1986). It is interesting to note that the vibration frequencies of the roofs (due to diaphragming motion) is similar to the walls but the damping of the roof structure is slightly lower for the diaphragming motion.…”

Environmental Assessment, Valentine Military Operations Area, Texax

“…Ashley (1976), examining blast effects in urban 3 areas, proposed peak particle velocities of 7.5 mm (0.3 in) and 12 mm (0.47 in)/sec for ancient and historic monuments and housing in poor repair, King et al (1985) note that the generally accepted view in Germany, Great Britain, and Sweden is that historic structures and archeological sites 3 should not be subjected to even minor, artificially 1iduced ground motions.…”