Let’s solve this step by step.
We are told:
- The P-wave travels
8000 km.
- It arrives at the seismic station at
11:40 am.
- We need to find the
origin time of the earthquake — that is, when the earthquake actually started.
To do this, we need to know how long it took the P-wave to travel 8000 km. That’s called the
travel time.
Looking at the graph (which shows travel time vs. distance for P-waves and S-waves):
→ Find
8000 km on the bottom axis (Epicenter Distance).
Note: The x-axis says “×10³ km”, so 8 means 8 × 1000 = 8000 km.
→ Go straight up from 8 on the x-axis until you hit the
P-wave curve (the lower one labeled “P”).
→ Then go left to read the travel time on the y-axis (Travel Time in minutes).
At 8000 km, the P-wave travel time is
12 minutes.
So, if the wave arrived at 11:40 am, and it took 12 minutes to get there, then the earthquake must have started
12 minutes earlier.
Now subtract 12 minutes from 11:40 am:
11:40 minus 12 minutes =
11:28 am
✔ Double-check:
If quake starts at 11:28 am, and P-wave takes 12 min to travel 8000 km → arrives at 11:40 am. Perfect match.
Final Answer:
11:28 am
Parent Tip: Review the logic above to help your child master the concept of earthquake p wave and s wave travel time worksheet.
