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Unpublished Paper
PALEOSEISMICITY OF QUATERNARY FAULTS NEAR ALBUQUERQUE, NEW MEXICO: The Zia Fault
USGS NEHRP Grant 99HQGR0056, Final Technical Report (2001)
  • James P. McCalpin
Abstract
This study continues USGS-funded efforts to assess the activity and earthquake hazard potential of Quaternary faults in the Albuquerque metropolitan region. Our target in 2000 was the Zia fault, a 37 km-long normal fault that trends N-S in northern Llano de Albuquerque (LdA). The Zia fault is one of three major east-dipping normal faults that define the western margin of the Rio Grande rift in the northern Albuquerque basin, the other faults being the Calabacillas fault (to the west of the Zia fault) and the County Dump fault (to the east of the Zia fault) (Machette et al., 1998). In the past 0.5-1.5 Ma, subsequent to the abandonment of the LdA surface by the Rio Puerco and Rio Grande, vertical displacement on the Zia fault has created at 20 m-thick syntectonic depositional wedge that is presently exposed by erosion on the Ceja de Rio Jemez at the northern rim of the LdA. Our trenches were located about 250 m south of the northern rim of the LdA, where a 100 m-wide graben has formed east of the main, 5 m-high fault scarp. The graben axis is not a closed depression and is currently drained by small ephemeral streams. The middle trench across the steepest, highest part of the scarp reveals evidence for at least 5 faulting events. Displacement in these events ranged from 0.6 to 2.6 m, with an average of 1.3 m. However, the age of the events is ambiguous due to wide disparities between two different types of age estimates. According to Wells and Coppersmith (1994), historic normal-fault earthquakes that have created fault scarps with an average height of 0.6-2.6 m range in magnitude from M6.6 to M7.0. The average displacement of the 5 inferred events in the middle trench (1.3 m), if assumed to be an average displacement, implies a magnitude of M6.85. This magnitude is identical to that which would be inferred from the length of the 32 km fault (Machette et al., 1998), which is also M6.85 according to Wells and Coppersmith (1994). Due to the conflict between the OSL and soil-carbonate dates, any conclusions about recurrence interval must be tentative. If one believes the soil-carbonate dates from the surface soil and younger buried soils are accurate, then the recurrence interval between Events Z and Y was 11 ka. The ages of the older event horizons (X, W, and V) and thus the length of previous recurrence cycles, cannot be estimated from soil carbonate due to erosion and missing section. However, a long-term average recurrence can be estimated if we assume that inferred 5 events have occurred since the formation of buried soils 5 and 6, which have a soil carbonate date of >63 ka and an OSL age of 119 ka. If the latest event occurred at 11 ka, then the four preceeding recurrence cycles spanned 52-108 ka, which yields an average recurrence interval of 10-21 ka.The five events inferred from the middle trench have a cumulative down-to-the-east throw of ca. 6.5 m. If that throw accumulated over the past 63-119 ka, then the average long-term slip rate is 0.055-0.1 mm/yr. This slip rate is greater than that inferred for the two other major faults on the LdA, the County Dump fault (0.016-0.018 mm/yr) and the Calabacillas fault (0.0053-0.0072 mm/yr).
Keywords
  • active fault,
  • New Mexico,
  • Albuquerque
Publication Date
2001
Citation Information
James P. McCalpin. "PALEOSEISMICITY OF QUATERNARY FAULTS NEAR ALBUQUERQUE, NEW MEXICO: The Zia Fault" USGS NEHRP Grant 99HQGR0056, Final Technical Report (2001)
Available at: http://works.bepress.com/james_mccalpin/14/