The thickness of upper mantle discontinuities (at depths around 410 km and 660 km) provides a critical clue to our understanding of deep earth. Since the amplitude of reflected or S‐P converted waves is controlled by the thickness of discontinuities, short‐period studies of such waves may give a fine constraint on the thickness of upper mantle discontinuities. In this study, we analysed short‐period and vertical waveform data from 14 deep events in the Fiji‐Tonga region. The data were obtained from J‐Array, a short‐period and large‐aperture seismic array in Japan. With slant stack analyses of these data, we detected short‐period reflections or S‐to‐P conversions from 410 km and 660 km discontinuities near sources, which implies that both discontinuities are quite sharp. To directly measure the frequency content of these waves, linear slant stacks were made with various frequency pass‐bands (0.2-0.5, 0.5-1.0 and 1.0-2.0 Hz). Synthetic traces were generated for the models with various thicknesses of the 410 km and the 660 km discontinuities. Comparison of slant stacks with synthetic traces indicates that the thickness of both discontinuities is at most 5 km.
2900 km thick
lithosphere
The upper mantle
The asthenosphere is typically around 100-200 kilometers thick beneath the Earth's crust. It is a semi-fluid layer of the upper mantle that allows for the movement of tectonic plates.
The layer located just below the mantle is the outer core. It is composed of a liquid layer of iron and nickel that surrounds the solid inner core of the Earth.
it's 410km to 660km thick
about 20 inches
about 20 inches
In oceanic areas the upper mantle is usually 5-200km thick and on continental areas it is 75-300km deep.
2900 km thick
The thickness of the Earth's mantle is about 2900 km and it's upper boundary is about 100km deep. There is a really cool cutaway drawing available by using the Wikipedia link.
The lithosphere, which includes the crust and upper part of the mantle, is typically around 100 kilometers thick beneath the oceans and up to 200 kilometers thick beneath the continents.
The outer core of the mantle can be liquid.
upper mantle
The main difference between the upper and lower mantle is their depth within the Earth. The upper mantle is located closer to the Earth's surface, extending from the crust to a depth of about 410-660 km, while the lower mantle lies beneath the upper mantle, extending from around 660-2,891 km deep. Additionally, the upper mantle is more rigid and composed of mainly solid rock, while the lower mantle experiences higher pressures and temperatures, leading to more plastic behavior.
This layer is about 163 miles thick below the earth.
The lower mantle is approximately 2,900 kilometers thick and extends from a depth of around 660 kilometers to 2,900 kilometers beneath the Earth's surface. It is composed mainly of solid rock that exhibits solid-state flow over geological timescales.