**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:*

*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**

**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**

**HOW TO FIND ORIGIN TIME**

**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. **

**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.**