<p>No, there isn't, because the area affected depends on so many factors, some of them unknowable. Magnitude, cause, depth, geology (which may be very variable in different parts of the area) etc. Besides which, the easiest way to tell which areas are affected is to monitor reports from observers. In the final analysis, the data that aid agencies want to know is which areas ARE affected rather than which might theoretically be affected if all relevant factors were known, which they rarely will be.</p>

CC BY-SA 4.0
2019-08-14T10:34:38.043Z
2019-08-14T10:34:38.043Z
Michael Walsby
<p>Yes, using GMPES. E.g., you can look at the USGS <a href="https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/shakemap/intensity" rel="nofollow noreferrer">shakemap</a> which includes some measure of intensities such as PGA/PGV. Just choose an appropriate cut-off value and you have your area.</p>

CC BY-SA 4.0
2019-09-12T19:50:49.073Z
2019-09-12T20:25:09.183Z
2019-09-12T20:25:09.183Z
stali
<p>If you visit <a href="https://earthquake.usgs.gov/earthquakes/browse/" rel="nofollow noreferrer">USGS earthquakes listing</a>, you get 3 points of information for each earthquake: Location, depth, magnitude. My question is, is there a way to approximate how big of an area is affected? Like if an earthquake happens 20km from San Francisco, how strong does it have to be for someone in SF to be able to feel it? </p>

CC BY-SA 4.0
2019-08-15T18:35:50.740Z
The inverse square law maybe.
John
CC BY-SA 4.0
2019-08-15T19:40:56.813Z
There is a relationship between the magnitude of the earthquake and the length of the fault rupture. See, for instance: https://www.usgs.gov/faqs/can-megaquakes-really-happen-a-magnitude-10-or-larger?qt-news_science_products=0#qt-news_science_products . There's some more information here: https://earthquake.usgs.gov/learn/topics/mag-intensity/ that includes some simple equations you might find interesting.
rchuso
<earthquakes><models><mathematics>
Is there a general equation to know how big of an area is affected by an earthquake?
Xyzk
# Is there a general equation to know how big of an area is affected by an earthquake?

(Asked by: username_0 on 2019-08-13)

If you visit [USGS earthquakes listing](https://earthquake.usgs.gov/earthquakes/browse/), you get 3 points of information for each earthquake: Location, depth, magnitude. My question is, is there a way to approximate how big of an area is affected? Like if an earthquake happens 20km from San Francisco, how strong does it have to be for someone in SF to be able to feel it?

**Tags:** earthquakes, models, mathematics

> **Comments:**
> **username_1**: The inverse square law maybe.  
> **username_2**: There is a relationship between the magnitude of the earthquake and the length of the fault rupture. See, for instance: https://www.usgs.gov/faqs/can-megaquakes-really-happen-a-magnitude-10-or-larger?qt-news_science_products=0#qt-news_science_products . There's some more information here: https://earthquake.usgs.gov/learn/topics/mag-intensity/ that includes some simple equations you might find interesting.  

---

## 2 answers

### Answer by username_3 on 2019-08-14. Score: 4 | Accepted answer

No, there isn't, because the area affected depends on so many factors, some of them unknowable. Magnitude, cause, depth, geology (which may be very variable in different parts of the area) etc. Besides which, the easiest way to tell which areas are affected is to monitor reports from observers. In the final analysis, the data that aid agencies want to know is which areas ARE affected rather than which might theoretically be affected if all relevant factors were known, which they rarely will be.


---

### Answer by username_4 on 2019-09-12. Score: 1

Yes, using GMPES. E.g., you can look at the USGS [shakemap](https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/shakemap/intensity) which includes some measure of intensities such as PGA/PGV. Just choose an appropriate cut-off value and you have your area.


---

