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<br />){ CONTENTS
<br />well-built wooden structures and bridges, some destroyed.
<br />Developed dangerous cracks in excellent brick walls. De-
<br />stroyed mwt masonry and frame structures, also tbeir foun-
<br />dalioru. Bent railroad rails slightly.~Tore apart, or crushed
<br />endwise, pipe lines buried in earth. Open cracks and broad
<br />wavy folds in cement pavements and sryhalC road surfaces
<br />XI. Disturbance is ground many end w-idr<pread, varying with
<br />ground ma4rial. Broad fissure, earth slumps, and land
<br />slips in soR, wet ground. Ejected water in lazge amounts
<br />charged with sand and mud. Caused sea-waves ("tidal"
<br />waves) of signiflcant magnitude. Damage severe to wood-
<br />frame structures, especially near shark ten4ra Great to
<br />dams, dikes, embankments often for long distances Few, if
<br />any (masonry) structures remained standing. Destroyed
<br />large well-built bridge by the wrecking of supporting pien,
<br />or pillars. Affected yielding wooden bridges less. Bent rail-
<br />road rails greatly, and throat them endwise. Put pipe lines
<br />buried in earth comple4ly out of senice.
<br />XII. Damage total-preMicelly all works of construction damaged
<br />greatly or destroyed. Disturbances in ground great and var-
<br />ied, eumerous shearing cracks. Lands) ides, falls of rock of
<br />eignificent chazac4r, slumping of ricer banks, etc., numer-
<br />ous and ex4nsive. Wrenched loose, tore o(f, large rock
<br />masses Fault slips infirm rock, with mtable horizontal and
<br />vertical onset displacements. Wa4r channels, surface and
<br />underground, disturbed end modified greatly. Dammed
<br />lakes, produced we4rfalls, deflected riven, ate. Weees seen
<br />on ground surfaces. Distorted lines of sight and level. Threw
<br />objects upward into the air.
<br />Interface. The common surface separating two different geologic
<br />media in Contact
<br />Internal friction. The resisting shear strength considered to be due
<br />to the ia4rlacking of the soil grains and the resistance to sliding
<br />between the grains.
<br />Isotropic. Having the same physical properties regazdless of the
<br />direction in which they aze measured. Strictly applies only to an
<br />arbitrarily small neighborhood surrounding a point and to single
<br />properties.
<br />Lama's constants. See Modulus.
<br />Least squares fit An analytic function a-hich approxima4s a set of
<br />data with a curve such that the sum of the squares of the distances
<br />from the observed points to the curve is a minimum.
<br />Linear ays4m. A sys4m whose output is linearly related to its
<br />input. If a linear sys4m is exci4d by a an input sine wave of
<br />Gequeney („ the output will contain only the frequency /;; the
<br />amplitude and phase may be changed.
<br />Linear viscoelastic medium. A medium (or ahich the functional
<br />relation between stress end strain can be expressed as a linear
<br />relation between stress, strain and their nth order temporal de-
<br />rivatives.
<br />Liquefaction Temporary Crans(ormation of cnconsolidated mate-
<br />rials into a fluid mass during an earthquake.
<br />Lithology. The description of rock composition and texture.
<br />Lithosphere. The cruet and upper mantle of the earth.
<br />Loading. The force on an object or structure or element of a strvc-
<br />lure.
<br />Longitudinal wave. Equals compression wave; equals P-wave.
<br />Love wave. A seismic surface wave which propagates in a surface
<br />layer. The vibration is transverse to the direction of propagation
<br />with no vertical motion.
<br />Low-cut fi14r. Equals high pass fi14r: A fi14r that transmits fre-
<br />quencies afwve a given colon frequenry and substantially at-
<br />4nua4s lower frequencies.
<br />Low-pass fl14r. Equals high•cut fil4r: A fi14r that transmits fre-
<br />que~v ~es below a given cutoff frequency and substantially alten-
<br />uetes all others. The earth acb like a low-pas, fi14r.
<br />Magnitude. A quantity that is characteristic oC fhe total energy
<br />released by an earthquake, as contrasted W in4nsity, which sus
<br />jectia'ely describes earthquake eRecb at a particular place. Profes-
<br />sor C. F. Rich4r devised the logarithmic magnitude scale in
<br />current use to define local magnitude (Sfc) in terms of the motion
<br />that would be measured by a standard type of seismograph located
<br />100 km from the epicn4r of en earthquake Several other mag- ,
<br />nitude scales are in use, for example, body-wave magnitude (msl
<br />and surfete-were magnitude (!N,) which utilize body waves and
<br />surface waves. The stale is open ended, but the largest known
<br />earthquake magnitudes (M,) ere near 8.9.
<br />Major principal stress. (See Principal stress) The largest (with
<br />regard to sign) principal stress.
<br />Mantle. The part of the earth's in4rior between the core and the
<br />crust The upper surface of the mantle is the Mohoroaicic dis-
<br />continuity.
<br />Meizoseismal zone. Zone of in4nse shaking in the neaz field of an
<br />earthquake. The radial width of this mne increases with mag-
<br />nitude.
<br />Mesosphere. The lower mantle. it is not involved in the earth';
<br />tectonic processes.
<br />Microtremor. A weak tremor.
<br />Minor principal stress. (See Principal stress). The smallest (with
<br />regard to sign) principal stress.
<br />Model A concept from which one can deduce effects that can then
<br />be compared to observations; this concept assists in understanding
<br />the significance of the observatiorv. The model may be conceptual,
<br />physical , or mathematical.
<br />Modulus. A measure of the elastic properties of a material. Moduli
<br />for isotropic bodies include:
<br />1. Bulk modulus, k. The stress-strain ratio under simple hydro-
<br />static pressure: the bulk modulus can be expressed in firms of
<br />other moduli as:
<br />
<br />2. Sheer modulus. Equals rigidity modulus, equals Lama's con-
<br />stant, µ: The stress-strain ratio for simple shear. The shear
<br />modulus can also be expressed in firms of other moduli and
<br />Poisson's ratio o as:
<br />__ E
<br />µ 211+0)
<br />3. Young's modulus, E. The stress-strain ration when a rod is
<br />pulled or compressed.
<br />4. Lama's constant A. If a cube is stretched in the up~direclion be
<br />a 4nsile stress, S, is giving an upward strain, s, and S' is the
<br />lateral 4nsile stress needed to present la4ral contraction,
<br />then:
<br />A=S'/s .
<br />This constant can also be expressed in terms of Young's
<br />modulus, E, and Poisson's ratio, v
<br />A= E o
<br />(1+0) (1-20-)
<br />The velocities of P-and Swaves, V, and V.„ can be expressed
<br />in firms of the moduli and the density, p:
<br />V, = s/(A+2µ)1p
<br />Vs = s~µ/p .
<br />Modulus of elasticity. The ratio of stress to strain for a material
<br />
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