Mid-Atlantic Power Pathway Chalk Point Substation to Indian River ...

Mid-Atlantic Power Pathway Environmental Review Document
Chalk Point Substation to Indian River Substation Volume II – Environmental Analysis of
April 13, 2011 Chalk Point Substation to MD/DE State Line
1.1.1.3 Geologic Hazards
Geologic hazards in the region crossed by the Project are minor and include areas of low to moderate
seismic activity and low incidence of landslides. Karst terrain and areas with the potential for ground
failure due to subsidence, slumping, and landslides are not common in the Project area. Volcanism is not
relevant to the region surrounding the Project and is not evaluated here (National Atlas 2009).
1.1.1.3.1 Seismicity and Faults
Seismicity refers to the geographic and historical distribution of earthquakes. Faults are fractures in rock
that provide evidence of past geologic movement. Earthquakes are caused by stress building up along a
fault until a critical limit is reached and the stress is released through sudden movement along the fault,
causing energy to radiate from the fault in traveling ground waves. Hazards associated with seismicity
and faulting include ground shaking, surface rupture of faults, and offset along normal, reverse, or strikeslip
faults. Faulting can be hazardous to linear, rigid structures such as bridges and pipelines, since the
ground could move in differing distances or directions at the fault.
Seismic activity can be described in terms of magnitude and intensity, where magnitude characterizes the
total energy released, and intensity describes impacts on a site-specific basis. The magnitude of a seismic
event is most commonly measured by the Richter Magnitude Scale, where the magnitude of the event is
expressed in whole numbers and decimals. The scale runs from a 1.0 to 8.0+, with 5.0 being considered a
moderate event; 6.0 a strong event; 7.0 a major earthquake; and a devastating earthquake exceeding 8.0.
Events with a magnitude less than 3.5 are generally considered imperceptible to most persons and in most
situations.
Earthquakes do occur in Maryland; however, the seismic risk is considered low. The epicenter of 61
earthquakes has been documented in Maryland from 1756 through 2003. All of these were low intensity,
low magnitude earthquakes; the maximum magnitude was 3.7 on the Richter Magnitude Scale and most
were less than 3.0. The most recent was a magnitude 3.6 on July 16, 2010 centered approximately 54
miles north-northwest of the Project area near Rockville, Maryland. Additional earthquakes originating
in neighboring states can also occasionally be felt in Maryland.
In general, Maryland is part of a seismically quiet zone (MGS 2007c). Seismic risk maps by the USGS
and the MGS indicated low seismic risk (MGS 2007c; Peterson et. al., 2008; USGS 2007). The MGS
map characterizes “all but the northeastern corner of the state as a ‘region of negligible seismicity with
very low probability of collapse of the structure.’” Similarly, the entire Project area is located in an area
classified by the Uniform Building Code as Seismic Zone 1 where earthquake activity is considered to be
minor (U.S. Army Corp of Engineers [USACE] 1995).
Based on the linear distance from active fault zones and the overall geologic setting of the Project area in
Maryland, the geologic hazard associated with seismicity and faulting is not considered to be a significant
risk.
1.1.1.3.2 Soil Liquefaction
Soil liquefaction is a condition that occurs when loose, cohesionless, saturated soil (usually well-sorted
sand) is subjected to vibration or shock waves. During liquefaction, pore water inhibits grain-to-grain
contact, and the strength of the soil is greatly reduced such that the soil may act like a viscous liquid with
the ability to move and flow. Soil liquefaction can lead to landslides and earthflows, movement or failure
of foundations and footings, and mobility of buried objects.
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