Standard style of some physical quantities in earthquake science Physical quantity Meaning of physical quantity Correct form Note Ms Surface magnitude MS M is italic and capital, S is capital and subscript Mw Moment magnitude MW M is italic and capital, W is capital and subscript mb Body magnitude mb m is italic, b is subscript ML Local magnitude ML M is italic and capital, L is capital and subscript fc Corner frequency fc f is italic, c is subscript vS Velocity of S wave vS vP Velocity of P wave vP v is italic， S is capital and subscript v is italic, P is capital and subscript  Pi   is a constant, thus  should be regular, not italic in any case. ds Differential ds d is differential symbol, thus d should be regular, not italic; s is a variant, therefore s should be italic wave wave