Calculating Pga Max Value

CALCULATING PGA MAX VALUE

FOR SULAWESI REGION

By

Group 4

Kusmiarto, Bambang S, M, Syukril & Christanti N

Earthquake Indonesia is a country which lies in an area according to the

plate tectonic theory known as ring of fire. As a part of ring of fire, Indonesia facing the fact that it has frequently earthquake strikes.One of the active region In Indonesia is Sulawesi Region. It lies facing to plate Philippine and pacific plate, besides that the fault around the area makes the region so vulnerable to facing earthquake. An earthquake is the result of a sudden release of stored energy in the Earth's crust that creates seismic waves The magnitude of an earthquake is conventionally reported using the Richter scale or a related Moment scale

PGA

PGA (Peak Ground Acceleration) is a maximum ground movement velocity happened in a given location measured because of earthquake occurrence in a given time and considering magnitude, hypocenter and ground dominant period. Unlike the Richter magnitude scale, it is not a measure of the total size of the earthquake, but rather how hard the earth shakes in a given geographic area

Calculating PGAMeasuring PGA max value for Sulawesi Region . Obtaining earthquake occurrence data recorded

correspondent to observed area - Time of occurrence ( Year, Month, Date, Time of origin)-  Geographic location-  Depth-  Magnitude

The data we get is from www.neic.usgs.gov. from Year 1973 to 2009, has Magnitude from 3 RS and more, depth from 800 km to 0 km. The geographic location between 115 to 130 E, 10 S to 10 N

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Counting R value (distance from focus/hypocenter of earthquake to the observed location) by using formula :

R = [(x1-x2)^2+(y1-y2)^2+(z1-z2)^2]^0.5

Counting Ms Konversion by using formula :

Mw = 0.7813 Mb + 1.5175

Mb = 1.2690 Ms – 1.0436

Mw = Magnitude moment wave

Mb = Magnitude body wave

Ms = Magnitude Surface wave

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Counting PGA value by using formula :

PGA = b1[10^b2Ms][(R+25)^(-b3)]

b1 = 472.3

b2 = 0.278

b3 = 1.301

Ms = Magnitude

R = Distance from observed point to earthquake focus Determining the PGA max value Determining MMI Scale

IMM = 3,66 log (PGA) – 1,66

IMM = Intensitas Getaran Tanah dalam

(dalam skala MMI)

PGA = Peak Ground Acceleration

(dalam gal = cm/s^2)

All the Measurement is done by calculating using MS – Excell.

Developing PGA contour map

To develop PGA contour map, we use PGA max value in each observed grid points and interpolate them using GIS software. We divide PGA max value range into 23 interval scale to develop contour map

Determining B-Value

To determining B-Value we need an earthquake occurrence frequency data for each RS scale magnitude. For this purpose we set the magnitude interval for 0.5 RS. The data then set into graphic using MS Excell to shows the correlation. A linear trend line should be developed to show the correlation and from its equation obtaining B-Value

B- value

INTERVAL

MAGNITUDE NO.

(MS)

FREQUENCY LOG FREQ.

1 3.0 - 3.49 0 0.00

2 3.5 - 3.99 34 1.53

3 4.0 - 4.49 2557 3.41

4 4.5 - 4.99 16533 4.22

5 5.00 - 5.49 6336 3.80

6 5.50 - 5.99 437 2.64

7 6.00 - 6.49 96 1.98

8 6.50 - 6.99 32 1.51

9 7.00 - 7.49 4 0.60

10 7.50 - 7.99 1 0.00

11 8.00 - 8.49 0 0.00

12 8.50 - 9.00 0 0.00

Result The area suffered highest PGA is located in northern part of

Sulawesi along the Bollaang Mongondo Utara, and the two others are in Middle west of Sulawesi i.e: Palu, Majene, Poso and Banggai Island. And exposed by high PGA maybe because it is influenced by many earthquakes that occur mostly in the Filiphine Trench, while middlewest part mostly affected by earthquake that occur near the coast and beneath the island itself, The exposed of this location may be because of The fault in Middle Sulawesi and The Tectonic form with Pasifik Trench.

The MMI Scale indicating that the tremor felt to every body ( III) scale to big damage of the building ( VII) scale

Result

Calculation of B value resulting an equation y = -0.721x + 4.991 with R2 = 0.990. B-value is -0.721x (shown in Graphic. 1). The B value shows the possibility of earthquake occurrence in observed area. The higher B-value we have the higher possibility to have an earthquake strike. Comparing to B-value for that is 0.721 with highest PGA max value of 239.111 gal, we can assume that suffered more earthquake than but in less strength and The less frequency of earth quake but in greater strength.

Thank you