There are two types of body waves: compressional (P) waves and shear (S) waves. Primary waves (P-waves) travel the fastest, so they arrive at the recording station (seismograph) first. Secondary or shear waves (S-waves) travel slower than P-waves so they arrive second.
Modified frequency modulation (MFM) is an encoding scheme used by PC floppy disk drives and older hard drives.
A woman may also be referred to an MFM if she develops complications during pregnancy. An MFM may provide advice for care during labor and birth or assist with the delivery. An MFM may also provide care after the birth if there are complications, such as heavy bleeding, elevated blood pressure, diabetes, or seizures.