Glossary of terms used on map Explanation, within Pop-up Windows, and in Detailed Reports
Glossary terms used in definitions are shown in bold italics.
Steep slope formed directly from movement along a fault. In a large normal-faulting earthquake (where fault slip is dominated by vertical movement), the ground surface becomes vertically offset across the scarp.
Generic term for a length of fault that is in some way distinct from, but related to, an adjacent length of fault. Typically, section boundaries are defined on the basis of fault geometry or geomorphology, such as a gap in surface faulting or a significant change in strike. Sections may or may not generate earthquakes independent of fault movement on other sections.
Names given to faults in the database are subdivided into a four-part hierarchy—Fault Zone Name, Fault Name, Section Name, and Strand Name. A Section Name is applied to subdivisions of a fault zone (equivalent to faults in the database that have a letter appended to the structure number).
A length of fault characterized by synchronous rupture, for which paleoseismic data show that the timing of surface faulting differs from that of an adjacent length of fault. All fault segments can be generically referred to as sections, but not all sections have the requisite data to show that they rupture as independent segments.
Sense of Movement (heading in detailed report)
See Slip Sense.
Rate of fault movement obtained when the amount of displacement or offset is divided by time interval; common units of measure are millimeters per year (mm/yr). In Utah, nearly all active faults are normal faults (characterized by dip slip, where fault slip is dominated by vertical, rather than horizontal, movement), and the slip rate reported is typically the vertical slip rate.
Slip-Rate Category (heading in detailed report)
Slip rates in the Utah Quaternary Fault and Fold Database are assigned to one of four categories: (1) >5 mm/yr, (2) 1–5 mm/yr, (3) 0.2–1 mm/yr, and (4) <0.2 mm/yr. Note that whereas the Quaternary Fault and Fold Database of the United States contains faults having slip rates of >5 mm/yr, Utah has no faults in this slip-rate category.
Relative movement of the ground/rock on one side of a fault with respect to the other side; includes normal, reverse, thrust, right-lateral (dextral) strike slip, and left-lateral (sinistral) strike slip.
Names given to faults in the database are subdivided into a four-part hierarchy—Fault Zone Name, Fault Name, Section Name, and Strand Name. A Strand Name is applied to subdivisions of a fault or fault section.
Trend or bearing of an imaginary line marking the intersection of a planar geologic feature (such as a fault) with a horizontal surface. Strike is always perpendicular to the dip angle.
One of five time categories within which the most recent surface faulting or folding occurred, based on historical documentation or geologic evidence. The categories are (1) historical (<150 years), (2) latest Quaternary (<15,000 years), (3) late Quaternary (<130,000 years), (4) middle and late Quaternary (<750,000 years), and (5) Quaternary (<2.6 million years).
Following the U.S. Geological Survey, faults and folds in the Utah Quaternary Fault and Fold Database are classified as either Class A or Class B.
- Class A structures are those for which geologic evidence indicates Quaternary deformation of tectonic origin. Movement on these structures results from regional crustal stresses, and the movement is typically accompanied by earthquakes.
- Class B structures are those for which geologic evidence indicates Quaternary deformation, but either the structure is likely too shallow to be a source of significant earthquakes, or the evidence for a tectonic origin is not strong enough for the structure to be classified as Class A. Class B structures, which include faults of uncertain earthquake potential, may be related to processes such as salt deformation and dissolution, landsliding, lateral spreading, or subsidence following volcanic activity.
Number assigned to the fault or fold, within the range specified by the U.S. Geological Survey for each state; for example, the Wasatch fault zone is identified as structure number 2351. Numbers given to fault sections (see also Section Name) consist of a structure number and an appended letter (a, b, etc.); for example, the Salt Lake City section of the Wasatch fault zone is identified as structure number 2351f.
Synopsis (heading in detailed report)
Summary of information for the structure, and indication of level of study. For sectioned faults, the synopsis includes a general discussion of the fault as a whole followed by a brief overview of the individual sections.
Relating to, causing, or resulting from structural deformation in the Earth’s crust.