# Impedance

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In seismology, impedance of a rock layer is defined as the product of bulk density ρB and P-wave velocity VP:

${\displaystyle Z_{\mathrm {P} }=\rho _{\mathrm {B} }V_{\mathrm {P} }\ }$

The normal incidence (vertical) reflection coefficient between an upper layer i and a lower layer i + 1 is given by

${\displaystyle R_{i}={\frac {Z_{i+1}-Z_{1}}{Z_{i+1}+Z_{i}}}}$

The angle-dependent reflectivity is given by the Zoeppritz equation.

## Shear impedance

S-wave impedance is the product of bulk density and S-wave velocity

${\displaystyle Z_{\mathrm {S} }=\rho _{\mathrm {B} }V_{\mathrm {S} }\ }$

## Elastic impedance

Elastic impedance (EI) is an offset (or angle) dependent property for non-normal angles of incidence. It was first described by Connolly, 1999.

## P to S converted wave elastic impedance (PSEI)

Also called Shear wave impedance.