<p><strong>Yes</strong></p>

<p>The biggest controlling factors are:</p>

<ol>
<li>Distance</li>
<li>Velocity Model</li>
<li>Composition (though velocity model and composition are related)</li>
</ol>

<p>I believe you understand the first factor, so I will focus on the other two. The most common <strong>GLOBAL</strong> velocity model is PREM, which is depicted below(<a href="http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html" rel="nofollow noreferrer">Image Source</a>):</p>

<p><img src="https://i.sstatic.net/IA8k1.gif" alt="enter image description here"> </p>

<p>Velocity models basically assume the internal P and S velocity structure of Earth. If the crust is thinner than average in the area where the source is, the arrival times will be faster than if the crust is thicker than average, though depending on the distance this could be negligible. This is because seismic waves travel faster in than they do in the crust, so the least time tends to involve travel through the mantle. </p>

<p>The other controlling factor is composition, or in other words, heterogeneities within the earth. Depending on the composition the wave travels through, arrival times could be slower or faster. For example, imagine an interplate earthquake traveling through a subducting slab and into a seismometer: the arrival times are slower because the wave speed of lithosphere is slower than the wave speed of mantle. In fact, its these deviations from our velocity model predictions that help us find heterogeneity in the earth to begin with! This is essentially how we find our natural resources, though instead of using earthquakes as the source we use man made active seismic waves. </p>

CC BY-SA 3.0
2015-05-12T17:05:40.170Z
Note that the velocity model is just a guess about the *actual* velocity of  waves in the earth, which is what really determines travel time of seismic waves (unless we're talking about models). There are also other factors: wave mode (P, S, surface, etc), path taken (including refracted and reflected rays), anisotropy, stress, and so on. And as you say, they are interrelated.
Matt Hall
CC BY-SA 3.0
2014-05-04T05:43:06.117Z
2014-05-04T05:43:06.117Z
Neo
<p>Bit puzzled why it appears that seismic travel times from one location to another appears to just be a function of the distance, and not any other factors. </p>

<p><img src="https://i.sstatic.net/Ndo4M.jpg" alt="enter image description here"></p>

<p><strong>Do seismic travel times from one location to another differ based on factors other than distance?</strong></p>

CC BY-SA 3.0
2014-05-09T12:22:36.350Z
Could you please provide a reference for that figure?
Leo Uieda
CC BY-SA 3.0
2014-05-09T14:02:43.030Z
@LeoUieda: Here's the reference for the figure: [Constraints on seismic velocities in the Earth from traveltimes](http://gji.oxfordjournals.org/content/122/1/108); note that the figure was [generated by me based on the model provided by the reference](https://www.wolframalpha.com/input/?i=seismic+travel+times+from+equator+to+north+pole).
blunders
<geophysics><earthquakes><seismology>
Do seismic travel times from one location to another differ based on factors other than distance?
blunders
# Do seismic travel times from one location to another differ based on factors other than distance?

(Asked by: username_0 on 2014-05-04)

Bit puzzled why it appears that seismic travel times from one location to another appears to just be a function of the distance, and not any other factors.

![enter image description here](https://i.sstatic.net/Ndo4M.jpg)

**Do seismic travel times from one location to another differ based on factors other than distance?**

**Tags:** geophysics, earthquakes, seismology

> **Comments:**
> **username_1**: Could you please provide a reference for that figure?  
> **username_0**: @username_1: Here's the reference for the figure: [Constraints on seismic velocities in the Earth from traveltimes](http://gji.oxfordjournals.org/content/122/1/108); note that the figure was [generated by me based on the model provided by the reference](https://www.wolframalpha.com/input/?i=seismic+travel+times+from+equator+to+north+pole).  

---

## 1 answers

### Answer by username_2 on 2014-05-04. Score: 9 | Accepted answer

**Yes**

The biggest controlling factors are:

1. Distance
2. Velocity Model
3. Composition (though velocity model and composition are related)

I believe you understand the first factor, so I will focus on the other two. The most common **GLOBAL** velocity model is PREM, which is depicted below([Image Source](http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html)):

![enter image description here](https://i.sstatic.net/IA8k1.gif)

Velocity models basically assume the internal P and S velocity structure of Earth. If the crust is thinner than average in the area where the source is, the arrival times will be faster than if the crust is thicker than average, though depending on the distance this could be negligible. This is because seismic waves travel faster in than they do in the crust, so the least time tends to involve travel through the mantle.

The other controlling factor is composition, or in other words, heterogeneities within the earth. Depending on the composition the wave travels through, arrival times could be slower or faster. For example, imagine an interplate earthquake traveling through a subducting slab and into a seismometer: the arrival times are slower because the wave speed of lithosphere is slower than the wave speed of mantle. In fact, its these deviations from our velocity model predictions that help us find heterogeneity in the earth to begin with! This is essentially how we find our natural resources, though instead of using earthquakes as the source we use man made active seismic waves.

> **Comments:**
> **username_3**: Note that the velocity model is just a guess about the *actual* velocity of  waves in the earth, which is what really determines travel time of seismic waves (unless we're talking about models). There are also other factors: wave mode (P, S, surface, etc), path taken (including refracted and reflected rays), anisotropy, stress, and so on. And as you say, they are interrelated.  

---

