Digital Earthquake Recording

8/18/2019 Digital Earthquake Recording

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Earthquake Recording and its ParametersEarthquake Recording and its Parameters

Arjun Kumar


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Earthquake Waves Body Waves

P or Longitudinal waves(more prominent on vertical component)

S or Transverse waves(more prominent on horizontal component)

Surface Waves Love waves

Ra leigh waves

ImportantforEarthquake

location

11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 222 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


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!omponents o" #otion

$ or %ertical !omponent

EW !omponent &S !omponent

W E

N

S

Z (up & down)

11 22 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 223 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

'mportant "or Engineers


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Wa s to Record #otion

cceleration (cm sec*+) , high "requenc signals

%elocit ( cm sec*) ,, intermediate "requenc signals

-isplacement (cm) . low "requenc signals

1 21 2 33 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 23 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2


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Recording 'nstruments

nalog (!ontinuous)(/ilm0 Smoke Paper0 Paper)

-igital (at regular intervals)(various digital data storage devices)

Analog

Broad Band

Short Period

1 2 31 2 3 44 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 225 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


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T pes o" 'nstruments

Short period, sensitive to high "requenc signals (local earthquakes) 'ntermediate period, sensitive to intermediate "requenc signals(regional events)

Long period, sensitive to low "requenc signals(teleseismic events)

#odern 'nstrument 1road 1and, e*g* 2*23 to 42 5z(local0 regional and teleseismic events)

The instruments records the motion produced !r!t! mass systemdue to an earthquake!

"o these days instruments records the voltage required to hold

the mass system at place!1 2 3 41 2 3 4 55 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 226 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


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678ective o" Routine Processing

6rigin Time (9#T or 'ST)Location (Epicenter : 5 pocenter)

Size (#agnitude)

Source Parameters (#oment0 Energ Release0/ault -imension0 Slip0 Stress -rop etc* )Tomography o" the Earth*

and man more;;*

EarthquakeParameters

dvanced Processing

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Time #IST or $%T&

Wadti-Diagram

S'

S(

S) S( S'

S)

Estimation o" 6rigin Time

1 2 3 4 5 61 2 3 4 5 6 77 8 9 10 11 12 13 14 15 16 17 18 19 20 21 228 9 10 11 12 13 14 15 16 17 18 19 20 21 22


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Recording Station

*ypocenter

Simple sketch o" arrival o" various phases

1 2 3 4 5 6 71 2 3 4 5 6 7 88 9 10 11 12 13 14 15 16 17 18 19 20 21 229 10 11 12 13 14 15 16 17 18 19 20 21 22


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Travel

Time!urve

1 2 3 4 5 6 7 81 2 3 4 5 6 7 8 99 10 11 12 13 14 15 16 17 18 19 20 21 2210 11 12 13 14 15 16 17 18 19 20 21 22


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Estimation o" Location

0.8)( ×−≅ P S d S(

S)

S'

By %ultiple Stations

0.10)( ×−≅ nn P S d

/or local earthquakes

/or regional earthquakes

d'

d(

d)

1 2 3 4 5 6 7 8 91 2 3 4 5 6 7 8 9 1010 11 12 13 14 15 16 17 18 19 20 21 2211 12 13 14 15 16 17 18 19 20 21 22


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Estimation o" Location

( ) N

E

A

A AZ 1tan1 −≅

S3

S+

By Single ) +omponent Stations

d+

d3

d) "

S

E W*

*

* *

$3

$+

S)

To Epicenter

1 2 3 4 5 6 7 8 9 101 2 3 4 5 6 7 8 9 10 1111 12 13 14 15 16 17 18 19 20 21 2212 13 14 15 16 17 18 19 20 21 22


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/irst rough discrimination a7out depth

22 km

h ? >22 km

1 2 3 4 5 6 7 8 9 10 111 2 3 4 5 6 7 8 9 10 11 1212 13 14 15 16 17 18 19 20 21 2213 14 15 16 17 18 19 20 21 22


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Estimation o" #agnitude

#agnitude is the measure o" the size o"the earthquake*

't is a num7er assign to a earthquake

't is independent of place of observation *

't is calculated "rom the amplitude o" theseismic waves o7served on aseismogram*

+ommonly used scales,

The Richter Scale 0 also called the Local #agnitude Scale ( # L)*

The body wave magnitude scale (m 7)*

The surface wave magnitude scale (# s)*

The duration magnitude scale (# - )*

The moment magnitude scale (# w)*1 2 3 4 5 6 7 8 9 10 11 121 2 3 4 5 6 7 8 9 10 11 12 1313 14 15 16 17 18 19 20 21 2214 15 16 17 18 19 20 21 22


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Richter magnitude scale/irst o" all0 merican seismologist !* /* Richter (3@>A) de"ined the magnitude scale7 listing the earthquakes occurred in Southern !ali"ornia recorded on Wood

nderson Seismograph*

5e de"ined the magnitude as natural log o" recorded trace amplitude recorded onstandard Wood nderson seismograph placed at an epicentral distance o" 322 km*

Disancemm A Log M L += )(10 correction factor

The equation 7ehind this monogram is92.2(sec)]8[log0.3)(log 1010 −∆+= t mm A M L

Pro-lems ith the Richter scale

This scale was originally intended to be sed only in a

!artic lar st dy area in "ali#ornia $ and on hori%ontal seis&ogra&s o# shallow earth' a es recorded on a !artic lar instr &ent$ the ood*+nderson seis&o&eter (,at ral #re' ency-1.12 %$ #ree !eriod - 0$ &a/.&agni#ication - 2800$ da&!ing #actor -0.80.

1 2 3 4 5 6 7 8 9 10 11 12 131 2 3 4 5 6 7 8 9 10 11 12 13 1414 15 16 17 18 19 20 21 2215 16 17 18 19 20 21 22


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The idea o" Richter magnitude scale was "urther eBtended "or earthquakes "rom di""erentregions and di""erent depth ranges equivalent 7od and sur"ace wave magnitude scalehave 7een developed C

Body ave magnitude #m - & . !alculated "rom short period 7od waves (D3 sec*)

The standard 7od ,wave magnitude "ormula ism 7 log32( A/T ) F G( D0h) 0 H1od wave magnitudeI

Surface ave magnitude #% s & . !alculated "rom long period sur"ace waves (D +2 sec*)

The standard sur"ace,wave "ormula is# S log32 ( T) F 3*JJ log32 (-) F >*>2 * HSur"ace Wave #agnitudeI

Sur"acewaves

1 2 3 4 5 6 7 8 9 10 11 12 13 141 2 3 4 5 6 7 8 9 10 11 12 13 14 1515 16 17 18 19 20 21 2216 17 18 19 20 21 22


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.uration magnitude #% . &

-ue to the ver limited d namic range o" analog and "ilm records (DK2 : J2d1)0 theevents occurred near to instrument clipp the records0 and hence determination o"magnitude 7ecomes impossi7le*

To cop this pro7lem0 7 cali7irating the total duration o" the signal o" earthquakes within322 km o" known magnitude # L0 duration magnitude is developed

M . /a 0 1 a ( log D

Where -M is total duration o" signal0 and constants a 2 and a 3 var "rom region to region*1 2 3 4 5 6 7 8 9 10 11 12 13 14 151 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1616 17 18 19 20 21 2217 18 19 20 21 22


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The major problem with magnitude scales based on Richter idea is that these are notrelated to physical characteristics of the earthquake source, there is a saturation effectnear !"# !$, owing to the scaling law of earthquake spectra!

%oment magnitude #% &

1 the 7eginning o" the +3st centur 0 a more ph sicall meaning"ul measurementcalled the seismic moment which is more directl relata7le to the ph sical parameters0such as the dimension o" the earthquake rupture0 and the energ released "rom theearthquake*

Mo = µ A D

'n 3@A@ seismologists Tom 5anks and 5iroo Nanamori0 proposed the momentmagnitude scale ( % w)0 which provides a wa o" eBpressing seismic moments in a "ormthat can 7e approBimatel related to traditional seismic magnitude measurements*

%w & '/" log ()*%o+ # ()!

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 161 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1717 18 19 20 21 2218 19 20 21 22


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!omparison o" %arious #agnitude Scales

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 171 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1818 19 20 21 2219 20 21 22


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Intensity#Based on 2-servation&

'ntensit measures the strength o" shaking produced 7 the earthquake at a certainlocation*'ntensit is determined "rom e""ects on people0 human structures0 and the naturalenvironment*/irst intensit scale was developed 7 Rossi,/orel* &owda s #odi"iel #ercalli and#SN intensit scales are generall used*

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 181 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1919 20 21 2220 21 22


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Intensity #cont3& 'ntensities t picall o7served near the epicenter o" earthquakes o" di""erent

magnitudes*

Magnitude / Intensity Comparison

Magnitude Typical MaximumModified Mercalli Intensity

1.0 - 3.0 I

3.0 - 3.9 II - III

4.0 - 4.9 I -

!.0 - !.9 I - II

".0 - ".9 II - I#

$.0 andhigher

III or higher

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%&erage pea'acceleration (g is

gra&ity)9.*m/s+s,

Modified Mercalli caleIntensity &alue and description

I. ,ot #elt e/ce!t by a ery #ew nder es!ecially #a orable circ &stances.( ossi* orel scale)II. elt only by a #ew !ersons at rest$ es!ecially on !!er #loors o# b ildings. 4elicately s s!ended ob ects &ay swing.( to ossi* orel scale)III. elt ' ite noticeably indoors$ es!ecially on !!er #loors o# b ildings$ b t &any !eo!le do not recogni%e it as anearth' a e. 6tanding a to&obiles &ay roc slightly. ibration li e !assing o# tr c . 4 ration esti&ated.( ossi* orel scale)

0.015g*0.02g I . 4 ring the day #elt indoors by &any$ o tdoors by #ew. +t night so&e awa ened. 4ishes$ windows$ doors dist rbed walls&a e crea ing so nd. 6ensation li e hea y tr c stri ing b ilding. 6tanding a to&obiles roc ed noticeably.( to ossi* orel scale)

0.03g*0.0 g

. elt by nearly e eryone$ &any awa ened. 6o&e dishes$ windows$ and so on bro en crac ed !laster in a #ew !lacesnstable ob ects o ert rned. 4ist rbances o# trees$ !oles$ and other tall ob ects so&eti&es noticed. :end l & cloc s &ay

sto!.( to ossi* orel scale)

0.0;g*0.07gI. elt by all$ &any #rightened and r n o tdoors. 6o&e hea y # rnit re &o ed a #ew instances o# #allen !laster and

da&aged chi&neys. 4a&age slight.( to ossi* orel scale)

0.10g*0.15g

II. < erybody r ns o tdoors. 4a&age negligible in b ildings o# good design and constr ction slight to &oderate in well* b ilt ordinary str ct res considerable in !oorly b ilt or badly designed str ct res so&e chi&neys bro en. ,oticed by

!ersons dri ing cars.( ossi* orel scale)1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 2121 2222


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%&erage pea'acceleration (g is

gra&ity)9.*m/s+s,

Modified Mercalli caleIntensity &alue and description

0.25g*0.30g

III. 4a&age slight in s!ecially designed str ct res considerable in ordinary s bstantial b ildings with !artial colla!segreat in !oorly b ilt str ct res. :anel walls thrown o t o# #ra&e str ct res. all o# chi&neys$ #actory stac $ col &ns$&on &ents$ walls. ea y # rnit re o ert rned. 6and and & d e ected in s&all a&o nts. "hanges in well water. :ersonsdri ing cars dist rbed.( = to > ossi* orel scale)

0.50g*0.55g

I#. 4a&age considerable in s!ecially designed str ct res well*designed #ra&e str ct res thrown o t o# !l &b great in

s bstantial b ildings$ with !artial colla!se. ? ildings shi#ted o## #o ndations. @ro nd crac ed cons!ic o sly. Andergro nd !i!es bro en.( > = ossi* orel scale)

Bore than 0.;0g

#. 6o&e well*b ilt wooden str ct res destroyed &ost &asonry and #ra&e str ct res destroyed with #o ndations gro nd badly crac ed. ails bent. Candslides considerable #ro& ri er ban s and stee! slo!es. 6hi#ted sand and & d. ater s!lashed$

slo!!ed o er ban s.(> ossi* orel scale)

#I. ew$ i# any$ (&asonry) str ct res re&ain standing. ?ridges destroyed. ?road #iss res in gro nd. Andergro nd !i!elinesco&!letely o t o# ser ice.


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Digital Earthquake Recording