LIQUEFACTION SUSCEPTIBILITY MAPPING IN THE METROPOLITAN ALBUQUERQUE REGION, NEW MEXICO

The Middle Rio Grande Basin near Albuquerque is within the seismically active Rio Grande rift, contains saturated Holocene floodplain deposits, and is vulnerable to liquefaction. Our mapping identifies areas that are susceptible to liquefaction based on integration of surficial geologic mapping, evaluation of shallow groundwater depths, and analysis of subsurface geotechnical data. This work provides 1:24,000-scale maps of the inner Rio Grande valley depicting: (1) surficial geologic deposits, (2) depth to groundwater, and (3) liquefaction susceptibility. The 4-km-wide Rio Grande valley is underlain by saturated, unconsolidated sandy alluvium associated with a complex pattern of paleochannels, point bars, and overbank levees formed by past Rio Grande courses. The valley also contains a network of artificial-fill levees along rivers and drainage ditches that may be susceptible to liquefaction. Because boreholes in the valley are spatially clustered, we compiled drive-point well data and water-level elevations from floodplain drainage ditches to expand the coverage of groundwater data. Present-day groundwater is shallow (generally <12 m), although many areas have experienced water-level declines resulting from substantial groundwater withdrawals during the past 50 years. For areas with sufficient subsurface geotechnical data, we used a modified Simplified Seed Approach to assess the liquefaction susceptibility of deposits. For areas without adequate subsurface data, we assessed susceptibility based on correlation of geologic units from areas with subsurface data. Most of the inner Rio Grande valley is susceptible to liquefaction, and large areas have Very High or High susceptibilities. Much of downtown Albuquerque is underlain by areas having High and Moderate susceptibilities. The areas of Moderate susceptibility are those most affected by historic water-level declines, suggesting that recent groundwater declines have helped decrease present-day liquefaction susceptibility. Notably, if future groundwater levels rise as a result of decreased groundwater pumping, some areas may become more susceptible to liquefaction. The map products from this study are useful for assessing liquefaction hazards and risk in the Middle Rio Grande Basin.