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.
What is MSM? Methylsulfonylmethane which is commonly known as MSM is a sulfur compound that naturally occurs and it is also a nutritional component found in a lot of food. It can be found in the normal diets of humans but the compound has become a popular dietary supplement.