![]() Nomenclature changed, such signals came to be called “teleseismic waves,” and they have been intensively studied especially for purposes of yield estimation in the context of the Threshold Test Ban Treaty. Seismac wave shadow zone verification#For the decades following the 1963 signing of the LTBT, when nuclear testing was carried out underground but no in-country verification was permitted, monitoring was conducted by National Technical Means using seismic signals acquired typically in the Third Zone. Amplitudes are relatively strong, out to distance ranges of around 1000 km (the First Zone) are weak or absent in the range around 1000-2000 km (the Shadow Zone) and become strong again beyond 2000 km (the Third Zone). Changes in the ocean, like formation of islands or submerging of existing islands due to earthquakes.The effect of variation in seismic wave speed with depth in the Earth (see bottom right), upon the path of propagation of the fastest seismic body waves (lower section, showing ray paths of propagation in the crust and upper mantle).Change in course of rivers : generally occurs due to tectonic upliftment or subsidence Ex: change in course of Mississippi river following the Madrid earthquake.Tsunami – an earthquake on the sea floor or close to the coast may cause huge waves.Landslides – earthquakes often cause landslides, especially in steep river valleys and areas of weak rocks.occurred in the Himalayan region during the recent Nepal Earthquake Avalanches : avalanche is a rapid flow of snow down a sloping surface.Liquefaction : when soils with a high water content are violently shaken they lose their mechanical strength and behave like a fluid and so buildings can literally sink.Shifting of landmasses – Sumatra shifting due to the earthquake of 2004.Subsidence: the earth‘s surface subsides or moves down in comparison to previous or sea level Ex : seen at many places in japan after 2011 Tohoku earthquake.Surface faulting – displacement of rocks along faults.primary and secondary effects causing much destruction the effects on the geography of a region includes Thus tomography can be used to outline the pattern flow in mantleĮarthquakes can be disastrous to humans as well as the environment. Hot parts of the mantle being less dense than their surroundings will rise, whereas cool mantle will sink. The tomography thus can be interpreted as “temperature maps”. SEISMIC TOMOGRAPHY – Here seismic waves are used as X-rays to analyse the velocity of seismic waves as they pass through earth in different directions with different temperatures.there is a huge shadow zone therefore outer core is liquid (as S-waves do not pass through liquid) zone where no P-waves are received between 103 & 143 deg. SHADOW ZONE- Refraction at the boundary between the core & the mantle thus causes a p-wave shadow zone over part of earth’s surface i.e.But seismic waves arriving sooner at distant stations & later at closer stations indicate that earth is not a homogeneous, uniform mass but has physical properties that change with depth. NON HOMOGENEOUS- If earth were homogeneous solid, seismic waves would travel in straight line with a constant speed.Seismic vibrations follow property of light waves being reflected & refracted with change in medium. ![]()
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