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- Earthquake_location abstract "The primary purpose of a seismometer is to locate the initiating points of earthquake epicenters. The secondary purpose, of determining the 'size' or Moment magnitude scale must be calculated after the precise location is known.The earliest seismographs were designed to give a sense of the direction of the first motions from an earthquake. The Chinese frog seismograph would have dropped its ball in the general compass direction of the earthquake, assuming a strong positive pulse. We now know that first motions can be in almost any direction depending on the type of initiating rupture (focal mechanism).The first refinement that allowed a more precise determination of the location, was the use of a time scale. Instead of merely noting, or recording, the absolute motions of a pendulum, the displacements were plotted on a moving graph, driven by a clock mechanism. This was the first seismogram, which allowed precise timing of the first ground motion, and an accurate plot of subsequent motions.From the first seismograms, as seen on the figure, it was noticed that the trace was divided into two major portions. The first seismic wave to arrive was the P-wave, followed closely by the S-wave. Knowing the relative 'velocities of propagation', it was a simple matter to calculate the distance of the earthquake.One seismograph would give the distance, but that could be plotted as a circle, with an infinite number of possibilities. Two seismographs would give two intersecting circles, with two possible locations. Only with a third seismograph would there be a precise location.The process of accurate location, was greatly improved with the advent of precise absolute timing. Early seismographs were almost always located at an astronomical observatory, just for the purpose of timing. See the history of the Canadian Dominion Observatory, is also the Geological Survey of Canada seismology laboratory. Recently, GPS is being used for accurate time, and seismometers can be located almost anywhere.Modern earthquake location still requires a minimum of three seismometers. Most likely, there are many, forming a seismic array. The emphasis is on precision, since much can be learned about the fault mechanics and seismic hazard, if the locations can be determined to within a kilometer or two, for small earthquakes. For this, computer programs use an iterative process, involving a 'guess and correction' algorithm. As well, a very good model of the local crustal velocity structure is required: seismic velocities vary with the local geology. For P-waves, the relation between velocity and bulk density of the medium has been quantified in Gardner's relation.".
- Earthquake_location thumbnail 1906_loma_prieta.png?width=300.
- Earthquake_location wikiPageID "3395441".
- Earthquake_location wikiPageLength "3271".
- Earthquake_location wikiPageOutDegree "24".
- Earthquake_location wikiPageRevisionID "617621350".
- Earthquake_location wikiPageWikiLink Astronomical.
- Earthquake_location wikiPageWikiLink Astronomy.
- Earthquake_location wikiPageWikiLink Bulk_density.
- Earthquake_location wikiPageWikiLink Category:Seismology_measurement.
- Earthquake_location wikiPageWikiLink Clock.
- Earthquake_location wikiPageWikiLink Displacement_(vector).
- Earthquake_location wikiPageWikiLink Dominion_Observatory.
- Earthquake_location wikiPageWikiLink Earthquake.
- Earthquake_location wikiPageWikiLink Epicenter.
- Earthquake_location wikiPageWikiLink Fault_mechanics.
- Earthquake_location wikiPageWikiLink Focal_mechanism.
- Earthquake_location wikiPageWikiLink Gardners_relation.
- Earthquake_location wikiPageWikiLink Geological_Survey_of_Canada.
- Earthquake_location wikiPageWikiLink Global_Positioning_System.
- Earthquake_location wikiPageWikiLink Moment_magnitude_scale.
- Earthquake_location wikiPageWikiLink Observatory.
- Earthquake_location wikiPageWikiLink P-wave.
- Earthquake_location wikiPageWikiLink Pendulum.
- Earthquake_location wikiPageWikiLink S-wave.
- Earthquake_location wikiPageWikiLink Seismic_hazard.
- Earthquake_location wikiPageWikiLink Seismic_velocity.
- Earthquake_location wikiPageWikiLink Seismic_wave.
- Earthquake_location wikiPageWikiLink Seismogram.
- Earthquake_location wikiPageWikiLink Seismometer.
- Earthquake_location wikiPageWikiLink Time.
- Earthquake_location wikiPageWikiLink File:1906_loma_prieta.png.
- Earthquake_location wikiPageWikiLinkText "Earthquake location".
- Earthquake_location wikiPageWikiLinkText "earthquake location".
- Earthquake_location wikiPageWikiLinkText "location".
- Earthquake_location hasPhotoCollection Earthquake_location.
- Earthquake_location wikiPageUsesTemplate Template:Reflist.
- Earthquake_location subject Category:Seismology_measurement.
- Earthquake_location comment "The primary purpose of a seismometer is to locate the initiating points of earthquake epicenters. The secondary purpose, of determining the 'size' or Moment magnitude scale must be calculated after the precise location is known.The earliest seismographs were designed to give a sense of the direction of the first motions from an earthquake. The Chinese frog seismograph would have dropped its ball in the general compass direction of the earthquake, assuming a strong positive pulse.".
- Earthquake_location label "Earthquake location".
- Earthquake_location sameAs m.099b9n.
- Earthquake_location sameAs Q5327273.
- Earthquake_location sameAs Q5327273.
- Earthquake_location wasDerivedFrom Earthquake_location?oldid=617621350.
- Earthquake_location depiction 1906_loma_prieta.png.
- Earthquake_location isPrimaryTopicOf Earthquake_location.