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Epicentral distance refers to the ground distance from the epicenter to a specified point. [1] Generally, the smaller the epicentral distance of an earthquake of the same scale, the heavier the damage caused by the earthquake. On the contrary, with the increase of epicentral distance, the damage caused by the earthquake is gradually reduced. [2]
Travel-time curve is a graph showing the relationship between the distance from the epicenter to the observation point and the travel time. [2] [3] Travel-time curve is drawn when the vertical axis of the graph is the travel time and the horizontal axis is the epicenter distance of each observation point. [4] [5] [6]
Knowing the relative 'velocities of propagation', it was a simple matter to calculate the distance of the earthquake. [4] 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.
This is why, in the 1989 Loma Prieta earthquake, the Marina district of San Francisco was one of the most damaged areas, though it was nearly 100 kilometres (60 mi) from the epicenter. [4] Geological structures were also significant, such as where seismic waves passing under the south end of San Francisco Bay reflected off the base of the Earth ...
It generally diminishes with distance from the earthquake's epicenter, but it can be amplified in sedimentary basins and in certain kinds of unconsolidated soils. Intensity scales categorize intensity empirically, based on the effects reported by untrained observers, and are adapted for the effects that might be observed in a particular region ...
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Vincenty's formulae are two related iterative methods used in geodesy to calculate the distance between two points on the surface of a spheroid, developed by Thaddeus Vincenty (1975a). They are based on the assumption that the figure of the Earth is an oblate spheroid, and hence are more accurate than methods that assume a spherical Earth, such ...
Web Mercator is a spherical Mercator projection, and so it has the same properties as a spherical Mercator: north is up everywhere, meridians are equally spaced vertical lines, angles are locally correct (assuming spherical coordinates), and areas inflate with distance from the equator such that the polar regions are grossly exaggerated.