# What does it mean when the depth of earthquakes get near the surface over a period of time?

First of all, I am not expert at this so correct me. My hometown is Shiraz and since last year I can sense the earth is moving. I call them mini earthquakes. But many people around me can not sense it. Some time ago there was an earthquake it felt like a 5 or even 6 richter earthquake but it was a 4 ricther earthquake but then in news they said that the depth was so close to the surface (4 km). I take a look at the USGS archives for Shiraz with in a 90 km diameter (as back in time as it was available) which I think will cover the major and minor fault lines. If you want to take a look its at a link! usgs archives[a] . And here is a diagram I made in excel.

This is depth diagram (horizontal axis is the time and starts from 1974). What is interesting for me is that the depth of the earthquakes broke the boundary of 10km and stayed there for a much longer than it used to.And here is the magnitude diagram

This is the map of major fault lines of Iran:

This is the same map (only the reverse fault lines):

And again the same map (only the lateral fault lines):

Is this a sign of fault lines building pressure? And why the depth of earthquakes are getting near the surface? Can a geologist make any kind of guess based on the pattern or this is not a pattern at all?

• Interesting question, thought you might want to know the link to USGS you referenced is not present currently, you might want to added it. Commented Jun 9, 2014 at 14:13
• @blunders changed the URL.It had so many parameters I couldn't add it,but now it's there. Commented Jun 9, 2014 at 14:23
• Thanks, the data and visualization from USGS was helpful, and posted an answer as a result. Let me know if it is of any use, or if somehow I have misunderstood the intent of your question. Thanks! Commented Jun 9, 2014 at 14:39
• Suggestion: To make the first graph clearer, consider putting the y-axis the other way up, so that deeper earthquakes are shown lower on the graph than shallower ones. Commented Jun 11, 2014 at 8:44
• "a 4 ricther earthquake but then in news they said that the depth was so close to the surface (4 km)" you can definitely feel a Mw 4 earthquake so shallow. If close enough (<5 or <10 km distance from the epicenter) you can feel even a magnitude 2 or 3. Commented Sep 7, 2021 at 11:36