Greg N. Mcdonald

Utah Geological Survey

The Utah Geological Survey (UGS) and the Idaho Geological Survey (IGS) mapped Quaternary-active faults in southeastern Idaho and northern Utah using recently collected airborne high-resolution topographic data in addition to available aerial photography and field reconnaissance. Specifically, the UGS and IGS mapped the East Bear Lake fault zone and...

How structural segment boundaries modulate earthquake behavior is an important scientific and societal question, especially for the Wasatch fault zone (WFZ) where urban areas lie along multiple fault segments. The extent to which segment boundaries arrest ruptures, host moderate magnitude earthquakes, or transmit ruptures to adjacent fault segments...

The 18 March 2020 Mw 5.7 Magna, Utah, earthquake was the largest earthquake in Utah since the 1992 ML 5.8 St. George earthquake. The geologic setting of the Magna earthquake is well documented by recent geologic mapping at 1:24,000 scale and 1:62,500 scale at and near the epicenter northeast of Magna, Utah. Subsurface fault modeling from surficial...

Rock avalanches are large-magnitude mass movements with high mobility and fluid-like runout; however, because of their scarcity, little information is typically available to describe the hazard posed by these events. Geologic records thus provide key data regarding rock avalanche size, timing, and dynamics. Here we present a detailed case history a...

Beginning in the mid-1800s, many settlers moved from east of the Mississippi River into the drier lands of the western United States. Water conveyance by canals and flumes was quickly adopted to ensure water supply for settlement needs and economic activities such as mining and agriculture. Many early canals were simply excavated or constructed wit...

The Nephi segment of the Wasatch fault zone (WFZ) comprises two fault strands, the northern and southern strands, which have evidence of recurrent late Holocene surface-faulting earthquakes. We excavated paleoseismic trenches across these strands to refine and expand their Holocene earthquake chronologies; improve estimates of earthquake recurrence...

An integrated approach involving field, laboratory and numerical investigations was undertaken to study the progressive deformation mechanism of a slope in glacial till above the Town of Alta, Utah that experienced catastrophic failure due to rapid snowmelt in June 2010. Detailed geometry of the slope surface and of the exposed sliding surface obta...

The Salt Lake City segment (SLCS) of the Wasatch fault zone (WFZ) and the West Valley fault zone (WVFZ) comprise Holocene-active normal faults that bound a large intrabasin graben in northern Salt Lake Valley and have evidence of recurrent, large-magnitude (M ~6–7) surface-faulting earthquakes. However, at the time of this investigation, questions...

The West Valley fault zone (WVFZ) and the Salt Lake City segment (SLCS) of the Wasatch fault zone comprise Holocene-active normal faults that bound an intrabasin graben in northern Salt Lake Valley, Utah, and have evidence of recurrent, large-magnitude (M ~6–7) surface-faulting earthquakes. Despite significant progress in our understanding of earth...

Of the five central segments of the Wasatch fault zone (WFZ) having evidence of recurrent Holocene surface-faulting earthquakes, the Brigham City segment (BCS) has the longest elapsed time since its most recent surface-faulting event (~2.1 kyr) compared to its mean recurrence time between events (~1.3 kyr). Thus, the BCS has the highest time-depend...

This report contains new paleoseismic information for the Weber segment of the Wasatch fault zone (WFZ), collected as part of a joint Utah Geological Survey and U.S. Geological Survey seismic-hazard evaluation. We excavated two fault trenches at the Rice Creek site in the spring of 2007 to address uncertainties in the number, timing, and displaceme...

As part of ongoing investigations of seismic hazards along the Wasatch Front, the Utah Geological Survey (UGS) has conducted the first paleoseismic investigation of the northern strand of the Nephi segment of the Wasatch fault zone at Santaquin, Utah. The Nephi segment consists of two strands (northern and southern) separated by a 5-km-wide right s...

Accurate slope-stability analysis of pre-existing landslides and adjacent, potentially landslide-prone slopes requires a realistic estimation of maximum ground-water levels. Previous researchers have documented a long-term rise in ground-water levels since the 1960s in unconsolidated deposits near recently active landslides. Ground-water levels ros...

INTRODUCTION At the request of Ron Chandler, the Utah Geological Survey (UGS) conducted a reconnaissance of the 1650 East landslide in the Highland View Estates subdivision, South Weber, Davis County, Utah (figures 1 and 2) on April 10, 2006. Rick Chesnut (Terracon) and Lee Cammack (JUB Engineers) were also conducting a field study of the landslide...

The meeting convened at 8:30 am with introductions. Ivan Wong (working group facilitator) gave a brief overview of the working group history, objectives, and accomplishments, and summarized last year's priorities and this year's objectives:  The Ground Shaking Working Group (GSWG) is at the point where urban seismic hazard maps (UHMs) need to be p...