[Familyofmonkeys]

Been reading up on earthquake risks for different areas of NZ. All I can find reference to is Modified Mercalli scale. I know what this is, where scale came from etc (got background in Geography).
What I can't find any reference to, is how this compares to Richter scale, and if there is a reason why one scale is given preference in NZ? Or are they measuring things very differently?

[Chiba]

Mercalli measures the physical effects of a 'quake on you and your stuff. Richter scale measures the magnitude of the quake event. In Japan we have something similar to the Mercalli scale. You can have a really large magnitude quake that happens very deep in the earth and a ways away and feel only few effects, but a low magnitude quake that's shallow and close by and you're in trouble.

[SteveR]

http://www.geonet.org.nz/earthquake/quakes/recent_quakes.html

lists all the recent and archived quakes data, you can check each quake drum and lots more info about the quakes in NZ

[aberdian]

They measure different properties of earthquakes

Richter Scale - measures the magnitude ie. how much energy was released at its focal point. This quantitative ie. measurable.

Modified Mercali Scale - measures the intensity ie. how much of the released energy is received at your location, which is dependent mostly on distance from source and the pathway to the source. This is a qualitative measure, developed in the 20th C and used by planners/engineers/insurance co's etc.

There is no linear relationship between the 2 scales, but they are interrelated. Big shake on the Richter scale a long way away may have the same value on the Mercali scale as a little shake close to home. :)

I was a geologist once, now I just pretend :)

Ian