## PSN-L Email List Message

Subject: Re: Earthquake strength
From: ChrisAtUpw@.......
Date: Tue, 8 Jul 2008 09:21:20 EDT

```In a message dated 2008/07/08, steinar@............. writes:

> That is, I'm assuming that the strength of an earthquake drops by the
> square of the distance. Is that a valid assumptation for earthquakes?

Hi Steinar,

The P and S waves are likely to fall off roughly as the cube of the
path distance through the Earth. Surface waves may initially decrease as the
square of the surface distance, but also increase in intensity as the source
approaches 180 degrees - the wave front is contracting in circumferance.

Regards,

Chris Chapman
In a me=
ssage dated 2008/07/08, steinar@............. writes:

That is, I'm assuming that the=20=
strength of an earthquake drops by the
square of the distance. Is that a valid assumptation for earthquakes?

Hi Steinar,

The P and S waves are likely to fall of=
f roughly as the cube of the path distance through the Earth. Surface waves=20=
may initially decrease as the square of the surface distance, but also incre=
ase in intensity as the source approaches 180 degrees - the wave front is co=
ntracting in circumferance.

Regards,

Chris Chapman
```