# Determining Arrival Times

IN THIS TYPE OF COMMON REGENTS QUESTION WE WILL BE ASKED TO FIGURE OUT WHEN A SEISMIC WAVE WILL BE DETECTED BY A SEISMOGRAPH.

TO DO THIS WE MUST BE GIVEN SOME INFORMATION:

• DISTANCE TO EPICENTER
• ORIGIN TIME OF THE EARTHQUAKE

## HOW TO FIND ARRIVAL TIMES:

### STEP 2:  ADD THE TRAVEL TIME TO THE ORIGIN TIME OF THE EARTHQUAKE

Let's Practice:  An earthquake occurs at 4:45:00 pm.  When will the P-wave arrive at a location 4,000 km from the epicenter?

Step 1:  Using the ESRT we can see that it takes a P wave 7 min 0 sec to travel 4,000 km.

Step 2:  4:45:00 + 0:07:00 = 4:52:00.

### The P wave will arrive at 4:52:00 pm

Let's Practice Another One:  An earthquake occurred at 2:28 am.  When will the P-wave arrive at a location 6,000 km from the epicenter?

Step 1:  Using the ESRT we can see that it takes a p wave 9 min 20 sec to travel 6,000 km.

Step 2:  2:28:00 + 0:09:20 = 2:37:20.

# Determining ORIGIN TIMES

IN THIS TYPE OF COMMON REGENTS QUESTION WE WILL BE ASKED TO DETERMINE WHAT TIME AN EARTHQUAKE OCCURRED.

TO DO THIS WE MUST BE GIVEN SOME INFORMATION:

• DISTANCE TO EPICENTER
• ARIVAL TIME OF THE WAVE

## HOW TO FIND ORIGIN TIME

### STEP 2:  SUBTRACT THE TRAVEL TIME FROM THE GIVEN ARRIVAL TIME

Let's Practice:  A P-wave is detected at 3:30:00 pm by a seismogram located 2,000 km from the epicenter.  When did the earthquake occur?

Step 1:  Using the ESRT we can see that it takes a p wave 4 minutes 0 seconds to travel 2,000km.

Step 2:  3:30:00 - 0:04:00 = 3:26:00

### The Earthquake occurred at 3:26 am.

Let's Practice Another One:  A S wave is detected at 8:55:40 pm by a seismic station that is 3,000km from the epicenter.  When did the earthquake occur?

Step 1:  Using the ESRT we can see that it takes an S wave 10 minutes to travel 3,000 km.

Step 2:  8:55:40 - 0:10:00 = 8:45:40

The Earthquake occurred at 8:45 and 40 seconds.