APPENDIX I GLOSSARY
| Active fault | In this EIS/EIR, a fault known to be recent
because it has displaced materials 35,000 years old or younger. Alquist-Priolo Special Studies Zones Act of 1972 defines an active fault as one that has had surface displacement during Holocene time (the last 11,000 years). |
| Alluvial | Referring to alluvium, which is any stream-laid sediment deposit found in a stream channel and in low parts of a stream valley subject to flooding. |
| Anticline | A fold in rocks in which the strata dip outward from both sides of the axis, where the oldest strata are in the core of the fold. The opposite of a syncline. |
| Arcuate | Curved like a bow, curved or bowed. |
| Aseismic slip | A slip along an underground fault consisting of many small movements so that very little seismic energy is emitted. |
| Blind thrust fault | A thrust fault that does not intersect the surface of the earth; a buried thrust fault. |
| Clastic | Pertaining to a rock or sediment composed principally of broken fragments that are derived from preexisting rocks or minerals and that have been transported some distance from their places of origin. |
| Colluvium | A general term applied to loose and incoherent deposits, usually at the foot of a slope or cliff and brought there chiefly by gravity. Talus and cliff debris are included in such deposits. |
| Conjugate fault | A fault or set of faults that are of the same age and deformation episode. |
| Coseismic slip | A slip directly associated with a particular earthquake, as opposed to a later slip. |
| Decollement | A low-angle fault that forms the base of an overlapping series of thrust faults. |
| Demand criteria | Values of maximum ground acceleration that buildings should be able to withstand and remain operational. |
| Deterministic | With results determined by input assumptions and data, but without the probability of occurrence. |
| Dextral motion | Right-lateral motion on a strike-slip fault. If one stands on one side of the slip, the other moves to the right. |
| Dip | The angle at which a stratum or other planar feature is inclined from the horizontal. |
| Disconformity | An unconformity in which the bedding planes above and below the break are essentially parallel, indicating a significant interruption in the orderly sequence of sedimentary rocks, generally by a considerable interval of erosion (or sometimes of nondeposition), and usually marked by a visible and irregular or uneven erosion surface of appreciable relief. (An unconformity is a substantial break or gap in the geologic record where one rock unit is overlaid by another not next in the stratigraphic succession.) |
| En echelon | Parallel structural features that are offset like the edges of shingles on a roof when viewed from the side. |
| Epicenter | The point on the earth's surface directly over the point at which earthquake motion starts. |
| Exponential notation | A means of expressing large or small numbers in powers of ten. For instance, 4.3×106 = 4,300,000 and 4.3×10-5 = 0.000043. This relationship is also sometimes expressed in the form 4.3E+6 = 4,300,000 and 4.3E-5 = 0.000043. |
| Fault | A fracture in the earth's crust accompanied by displacement of one side of the fracture with respect to the other and in a direction parallel to the fracture. |
| Fault creep | Slow ground displacement usually occurring without accompanying earthquakes. It may be of tectonic origin or result from oil or ground water withdrawal. |
| Fault plane solution | A determination of the underground plane on which a slip occurs in an earthquake; a determination of the focal plane. The distribution of first-motion compressional and dilatational waves from an earthquake calculated from many seismological stations. |
| Fault zone | The region of rock failure along a fault. |
| Focal depth | The depth from the earth's surface to the point of initial rupture of an earthquake. |
| Focal plane | The plane on which the initial rupture of an earthquake occurs. |
| Fold | A bend in strata or any other planar structure. |
| g notation | Accelerations measured relative to the acceleration of gravity at the earth's surface. Thus, 0.1g = 3.2 ft/sec2 or 98.3 cm/sec2. |
| Geodetic | Of, relating to, or determined by geodesy, which is a branch of applied mathematics that determines the exact positions of points and the figures and areas of large portions of the earth's surface, the shape and size of the earth, and the variations of terrestrial gravity and magnetism. |
| Geologic ages | The ages of rocks, formations, etc. The present age is the Holocene or Recent Age. |
| Ground acceleration | The intensity of the strong phase of ground shaking in units of g (earth's gravitational attraction). |
| Holocene | A standard epoch of geological time, from 10,000 years ago until the present. |
| Left-lateral | On a strike-slip fault, if one stands on one side of the slip, the other moves to the left. |
| Liquefaction | A type of soil failure where a mass of saturated soil is transformed from a solid to a liquid state. |
| Magnitude | A measure of the strength of an earthquake or the strain energy released by it; the logarithm of the amplitude of motion recorded on a seismograph. |
| Metamorphic rock | Any rock derived from preexisting rocks by mineralogical, chemical, and/or structural changes, essentially in the solid state, in response to marked changes in temperature, pressure, shearing stress, and chemical environment, generally at depth in the earth's crust. |
| Microearthquakes | Very small earthquakes that can only be detected by seismometers. |
| Microseismicity | Weak seismic signals in an earthquake region that are too small to notice but which indicate continued slow slip. |
| Miocene | A standard epoch of geologic time between the Pliocene and Oligocene, from about 28 million to 5.3 million years ago. |
| ML | Local or Richter magnitude defined as the log10 of the maximum seismic-wave amplitude recorded on a standard seismograph at a distance of 100 km from the earthquake epicenter. The magnitude measures the strain energy released by an earthquake. |
| Modified Mercalli Scale | An earthquake intensity scale, with 12 divisions ranging from I (not felt by people) to XII (damage nearly total). |
| MS | Surface wave magnitude; magnitude determined from measurements of the amplitude of seismic surface waves. |
| Normal fault | A fault in which the block above appears to have moved downward relative to the block below. |
| Paleosol | A buried soil; a soil of the past. |
| Piercing point | A point at which an underlying structure penetrates to the earth's surface. |
| Plate tectonics | A theory of global-scale dynamics involving the movement of rigid plates of the earth's crust. |
| Pleistocene | A standard epoch of geological time, from about 1.6 million to 10,000 years ago. |
| Pliocene | A standard epoch of geological time, from about 5.3 million to 1.6 million years ago. |
| Plunge | The inclination of a linear geologic structure measured as the angle it makes with the horizontal. |
| Quaternary | The period of geologic time since the end of the Pliocene, comprising the Pleistocene and Holocene, from about 1.6 million years ago to the present. |
| Response spectra | Spectral content of earthquake accelerations for specified peak accelerations and damping factors. |
| Reverse fault | A fault dipping steeper than 45·, in which the block above appears to have moved upward relative to the block below. |
| Right-lateral motion | On a strike-slip fault, if one stands on one side of the slip, the other moves to the right. |
| Sedimentary rock | A rock resulting from the consolidation of loose sediment that has accumulated in layers. |
| Seeps | A spot where water or petroleum oozes from the earth, often forming the source of a small trickling stream. |
| Seiche | A wave oscillation of the surface of water in an enclosed basin (such as lake or bay) initiated by an earthquake or changes in atmospheric pressure. |
| Seismogenic source | A fault capable of producing earthquakes. |
| Shear | Force or motion tangential to the section on which it acts. |
| Slickensides | A smoothly striated surface that results from friction along a fault plane. |
| Slip | To move or displace; a movement dislocating adjacent blocks of crust separated by a fault. |
| Splays | Divergent small faults that comprise a fault zone. |
| Strata | Plural of stratum which is a single sedimentary bed or layer. |
| Stratigraphic offset | Displacement of a formerly continuous stratigraphic horizon. |
| Strike (of a fault) | The direction of the line of intersection of a horizontal plan with an uptilted geologic stratum. |
| Strike-slip fault | A fault in which the net slip is horizontal, parallel to the strike of the fault. |
| Surface faulting | As opposed to a thrust fault, a fault that does intersect the surface of the earth; the displacement of ground along the surface trace of a fault. |
| Syncline | A fold in rocks in which the strata dip inward from both sides of the axis, where the youngest strata are in the core of the fold. |
| Terraces | Relatively horizontal or gently inclined surfaces or deposit sometimes long and narrow, which are bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side. |
| Tertiary | The period of geologic time between the Cretaceous and the Pleistocene, comprising the Pliocene, Miocene, Oligocene, Eocene, and Paleocene, from about 65 million to 1.6 million years ago. |
| Thrust fault | A fault dipping less than 45·, in which the block above appears to have moved upward relative to the block below. |
| Tonal contrast | A contrast in color value or hue in a photograph. Often referred to a change or contrast in color along a linear trend in aerial photographs of the earth's surface, suggesting the presence of a fault or structural boundary. |
| Trace | A line on one plane representing the intersection of another plane with the first one (e.g., a fault trace). |
| Trend (of a fault) | Its strike. If the fault intersects the surface, the direction of that intersection. |
| Tuff | A rock formed of compacted volcanic fragments, generally smaller than 4mm in diameter. |
| Volcanic rock | A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the Earth's surface, either ejected explosively or extruded as lava (e.g., basalt). The term also includes near-surface intrusions that form a part of the volcanic structure. |
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