Seismic PGA Values

[NAFTALI-HAKOHEN]

hi,

a general question,

i once heard from a lecturer that Z (MAX PGA VALUES) are increased by the standards as the years go by , AND NO SERIOUS EARTHQUAKE HAS OCCURED...

the spring(TECTONIC PLATE) is wound tighter, leading to larger chance of larger earthquake - thus higher Z values

i can seem to find evidence corroborating this statement, does anyone know anything about this?

thanks

NAftali