science

Travel-time curve

Travel-time curve is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Travel-time curve rather than just read about it. In short: Travel time in seismology means time for the seismic waves to travel from the focus of an earthquake through the crust to a certain seismograph station. Travel-time curve is a graph showing the relationship between the distance from the epicenter to the observation point and the travel time.

Key takeaways

Travel-time curve belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Travel-time curve to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Travel-time curve from memory before moving on to harder problems.

Reference excerpt

Travel time in seismology means time for the seismic waves to travel from the focus of an earthquake through the crust to a certain seismograph station. Travel-time curve is a graph showing the relationship between the distance from the epicenter to the observation point and the travel time. Travel-time curve is drawn when the vertical axis of the graph is the travel time and the horizontal axis is the epicenter distance of each observation point. By examining the travel-time curve, it is possible to know the seismic wave velocity and the depth of the epicenter and so on. It also provides clues to study the layered structure inside the earth. For example, by examining the travel-time curve of a teleseism, it can be seen that the earth consists of the crust, mantle, outer core, and inner core. Travel-time curve also shows the relationship that the surface wave arrives first at the point near the epicenter, and conversely the refracted wave arrives first at the point far from the epicenter. Seismic body waves (P- and S-waves) do not usually travel at a constant speed, as their speeds typically increase with depth in the Earth. The further the waves travel from the earthquake, the deeper they must go through the Earth. This results in the travel-time curves bending downward, indicating they take less time to travel a given distance. Surface waves (Love and Rayleigh waves are confined to the uppermost crust, so their speeds do not change with distance. The body wave speeds tend to change smoothly with depth, but at certain depths they experience an abrupt change, known as a seismic discontinuity. One example of this is when the waves pass from the crust into the mantle, where the wave speeds suddenly increase ~1 km/s, causing a change in the curvature of the travel-time curves. This particular discontinuity is known as the Mohorovic discontinuity, aka the Moho, discovered by Croatian seismologist Andrija Mohorovičić in 1909 when he examined distinct sets of P- and S-waves generated by an earthquake in Zagreb. He realized that this could only be due to waves traveling at different speeds due to a sudden change in density with depth.

See also Seismic wave Mohorovic discontinuity

References

Illustrations

Worked examples

Example 1 — a first encounter with Travel-time curve

Start with the simplest possible case. Write down what Travel-time curve claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Travel-time curve before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Travel-time curve ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Travel-time curve

In research: Travel-time curve appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Travel-time curve in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Travel-time curve is common in secondary-school and first-year university syllabi. It links to neighbouring topics Seismology, Seismology stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Travel-time curve outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Travel-time curve in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Travel-time curve means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Travel-time curve out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Travel-time curve in simple terms?

Why does Travel-time curve matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Travel-time curve?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Travel-time curve.