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Homework 3: Earthquakes & Volcanoes

Earthquakes: Southern Peru Earthquake, June 23, 2001

On June 23, 2001, a massive earthquake of moment

magnitude 8.4, the largest earthquake recorded

worldwide in 3 !ears, struck off the coast of southern

"eru. #ides$read structural damage was re$orted in

"eru%s second largest cit!, &requi$a, known for

historical colonial 'uildings. (andslides were common

in the mountainous regions, 'locking roads, disru$ting

communication lines, and contri'uting to the loss of

$ro$ert! and life. &fter re$airing roads and clearing

landslides, relief workers headed to )oquegua wherethe! found wides$read destruction. "reliminar!

estimates indicate at least 80* of the 'uildings weredestro!ed or ruined.

+umerous aftershocks were felt '! local residents. "reliminar! data indicated at least 33 aftershocks registered ).0 or

stronger, including three in the ) range- an ).3 a little more than a half an hour after the main shock, an ).2 at

21-3, and the largest, an ).8, at 04-18-32 on June 2. /t was the largest earthquake in "eru since a ). struck a'out

200 miles to the northwest on +ovem'er 12, 1. /t was the seventh ) earthquake to strike the $lanet in 2001 and

the largest since the intense olomon /slands )8.2, ).8 and ).2 earthquake series in +ovem'er of 2000.

Part 1: Locate the Epcenter

1. sing igure 1, record the arrival times of the " and waves at each station in 5a'le 1. 6ead each arrival timeas $recisel! as $ossi'le 7in minutes and estimated fraction of a minute. 5he first vertical line marks the "9wave

arrival and the second vertical line marks the 9wave arrival time.

!a"le 1# SP$ % Sao Paolo, $ral' H() % Here*a, )osta +ca' ( % ort *e rance, -artnque

Sesmo.raph

Staton

P/wae rral

mnutes

S/wae rral

mnutes

!me (44erence

S / P' mnutes

Epcenter (stance

kmSPB mins 1 sec mins 0 sec 4 mins 3 sec 2,800:;< mins 10 mins 10 sec 4 mins 10 sec 3,000; mins 30 sec 11 mins 0 sec mins 20 sec 3,200

2. ;etermine the 9" interval '! taking the 9wave arrival time minus the "9wave arrival time. 6ecord !our

results in 5a'le 1.

3. se !our and "9wave arrival times and igure 2 to determine the distance from each station to the e$icenter.

5here are 3 wa!s !ou can do this.

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1 =o to !our "9wave arrival time along the vertical a>is, move hori?ontall! until !ou intersect the " line, and

then go straight down to the hori?ontal a>is and record the ;istance to @$icenter.

2 ;o the same thing using !our 9wave arrival times and the line.

3 se !our 5ime ;ifference, and find the $lace on the gra$h where the and " lines are that amount of time

a$art, then go straight down to the hori?ontal a>is.

Aou should get a$$ro>imatel! the same answer for all 3 of these methods. ;onBt forget to multi$l! the num'ers

along the hori?ontal a>is '! 1,000 to get the correct distanceC

4. #hich station is located farthest from the e$icenterD "E :;< ;

10 20 !me mn#

.ure 1# Sesmo.rams 4rom three montorn. statons#

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.ure 2# rral tme cures 4or P an* S waes# 5ote that the horontal a6s s 10007s o4 km#

. On )a$ 1, the e$icenter distances were used to draw circles around each monitoring station. Eased on their

geogra$hic locations 7Era?il,


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. 5he intersection of all 3 circles marks the earthquake e$icenter. ;rag this arrow to $oint at the e$icenter on the

ma$.

. #h! is it necessar! to have seismograms from at least three monitoring stations to find the e$icenter of the quakeD

1

1 8t s nessesar9 "ecause the9 locate the epcenter "9 tran.ulaton# !he *stance s 4.ure* out "9 usn. the

arral tmes o4 sesmc waes o4 all three montorn. statons#

-ap 1# -ontorn. statons an* epcenter o4 the Peru earthquake

8. 5he earthquake occurred on a tectonic $late 'oundar!. 6efer to )a$ 2 to answer the following questions-

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SP$

(

H()


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a. Eetween which two $lates did the earthquake occurD

South mercan an* 5asca plate

'. &re the $lates moving towards one another, awa! from one another, or sliding $ast one anotherD

!he plates are mon. towar* one another

c. #hat t!$e of 'oundar! is thisD

)oner.ent "oun*ar9

-ap 2# !ectonc "oun*ares


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Volcanoes

or each of the volcanoes 'elow, choose its t!$e and magma viscosit! '! making the te>t "ol*.

Volcano !9pe -a.ma Vscost9

.

10.

11.

12. :ow does magma viscosit! affect the stee$ness of a volcanoD


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-ount Sant Helens Eruptons

.ure 3# Satellte ma.e o4 -ount St Helens "e4ore top an* a4ter "ottom the 1;0 erupton#

N

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13. 5ake a look at igure 3. #hen the volcano eru$ted, in what direction did the maGorit! of the de'ris goD1 5orth

14. #hen )ount t :elens eru$ted in 180, red hot lava did not s$ew out of the volcano and $our down its flanks. 6ather,

igure 4 shows the eru$tion and some of the destruction that occurred as a result of it. Eased on this information, list threevolcanic ha?ards that ma! occur from eru$tions at )ount t :elens.

1# sh

2#


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.ure @# Erupte hstor9 o4 -ount St Helens snce 1=00 (

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