Example preset
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Inputs
Results
| P wave running time | — |
|---|---|
| Omori coefficient k (this Vp/Vs conversion) | — |
| S wave running time | — |
| Occurrence time (P standard) | — |
| Occurrence time (S standard) | — |
| Difference in time of occurrence | — |
Graph (distance - running time)
Once entered, the travel time curve will be displayed.
How it's calculated
Assuming constant speed (Vp, Vs), the running time is tP = D / Vp、tS = D / Vs It is.
S-P = Δt = tS - tP Therefore, the epicenter distance D is calculated using the following formula.
D = Δt / (1/Vs - 1/Vp) = Δt × Vp × Vs / (Vp - Vs)
In school materials D = k × (S-P)(Omori official)k = Vp × Vs / (Vp - Vs) is the Omori coefficient.
In arrival time mode,T0 = Tp - D/Vp(P standard) and T0 = Ts - D/VsEstimate the time of occurrence from (S standard).
Attention:This tool is an approximation for learning and does not take into account depth dependence of velocity, crustal structure, or path differences.
FAQ
What is the initial tremor duration (S-P)?
This is the time difference between the arrival of P waves and the arrival of S waves. In general, the farther from the epicenter the longer S-P will be.
Are epicenter distance and epicenter distance the same?
Strictly speaking, it's different. This tool is an educational approximation that uses a simple model with a constant speed to estimate the epicenter distance.
How high should I set Vp and Vs?
Typical values are used in textbooks, but they vary depending on region and depth. Please give priority to the values specified in classes and materials.
What should I do if the S wave arrival time is smaller than the P wave?
If you want to cross dates, turn on "S wave the next day". Please also check the time as there may be a typo.
Can this result be used for disaster prevention decisions?
Cannot be used. This tool is an approximation for learning and educational purposes. Please refer to information from public institutions for actual judgment.
How to use Calculate epicenter distance and occurrence time from P waves and S waves (initial tremors) (for education) effectively
What this calculator does
This page is for estimating outcomes by changing inputs in one controlled workflow. The model keeps your focus on variables, not output shape. Start with stable assumptions, then test sensitivity by changing one key input at a time to observe directional impact.
Input meaning and unit policy
Each input has an expected unit and a typical range. For reliable interpretation, check whether you are using the same unit system, period, and base assumptions across all runs. Unit mismatch is the most common source of unexpected drift in numeric results.
Use-case sequence
A practical sequence is: first run with defaults, then create a baseline log, then run one alternative scenario, and finally compare only the changed output metric. This sequence reduces cognitive load and prevents false pattern recognition in early experiments.
Common mistakes to avoid
Avoid changing too many variables at once, mixing incompatible data sources, and interpreting a one-time output without checking robustness. A single contradictory input can flip conclusions, so keep each experiment minimal and document assumptions as part of your note.
Interpretation guidance
Review both magnitude and direction. Direction tells you whether a strategy moves outcomes in the desired direction, while magnitude helps you judge practicality. If both agree, you can proceed; if not, rebuild the baseline and verify constraints before deciding.
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