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
arrivaltime1.jpg

HOW TO FIND ARRIVAL TIMES:

STEP 1:  DETERMINE THE TRAVEL TIME USING THE ESRT AND THE GIVEN DISTANCE

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

arrivaltime2.jpg

 

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.

The p wave will arrive at 2:37 and 20 seconds am. 

 

 

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

 

 

eqtime1.jpg

HOW TO FIND ORIGIN TIME

STEP 1:  DETERMINE THE TRAVEL TIME USING THE ESRT

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. 

eqtime2.jpg

 

 

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.