Seismology for Civil Engineers

7/29/2019 Seismology for Civil Engineers

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CHAPTER 1

Seismology for Civil Engineers

1.1 INTRODUCTION

In a broad sense, the Earthquake Engineering is a part of engineering devoted to

mitigating earthquake hazards. From this point of view, it must provide means for

analyzing and solving the problems involved by damaging earthquakes. Therefore, the

civil engineers use Earthquake Engineering findings in all stages of earthquake-

resistant structures' existence: planning, designing, constructing, and managing.

From the point of view of a structural engineer, the Earthquake Engineering is

a part of Structural Dynamics concerned with the determination of the strain and

stresses state for the structures subjected to earthquakes, and it gives the ways to

optimize the earthquake-resistant structures.

Notions and knowledge from geophysics, geology, seismology, vibration

theory, structural mechanics, and construction techniques are needed in EarthquakeEngineering.

As a part of Geology, the Seismology is the science concerned with the study

of earthquakes (causes, propagation, recording, Earth's structure, generation

mechanisms, history, prediction, etc.).

Although there are many sources of external load that must be considered in

the design of civil engineering structures, the most important by far in terms of its

potential for disastrous consequences is the earthquake. During the human history, the

earthquakes had been a major source of fear because of the severe consequences

generated by strong earth shakings. Even during the 20th

Century seismic activity

caused many damages. Table 1.1 shows a list of such events that happened and the

losses of human life because of them from the year 1900 until now.

1.2 STRUCTURE OF THE EARTH

It is believed that the beginning of the Earth coincides with that of our galaxy, i.e.

approximately 4500 millions years ago. The nowadays Earth's body shape is formed

at the start of Paleozoic Era. Table 1.2 shows a geologic history of the Earth.

A general internal structure of the Earth is shown in Figure 1.1. Three main

spheres compose the Earth: the crust, the mantle, and the core. Each part has different

composition. The spheres from the Earth's structure are separated through

discontinuities. TheMohorovicic (orMoho) discontinuity is located between the crust

and mantle. It is strongly influencing the earthquake waves transmission mechanism.


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The crust may be classified into two distinct parts: the continental crustand

the oceanic crust. The first one is mainly composed from Silicon and Aluminum and

therefore it is also named SIAL. It has a density of about 2.7 g/cm3.

Table 1.1 A list of major earthquakes and life losses caused by them during the 20th Century

Year M Area,Country

DeadPeople

Year M Area,Country

DeadPeople

1906 8.3 San Francisco,

USA

700 1957 7.9 Mexico City,

Mexico

68

1908 7.5 Messina, Italy 120,000 1959 7.1 Hebgen Lake,

USA

28

1915 7.5 Avezzano, Italy 35,000 1960 8.3 Chile 1,743

1920 8.5 Kansu, China 100,000 1960 5.9 Agadir, Morocco 14,000

1923 7.9 Kanto, Japan 143,000 1962 7.3 Northwest Iran 12,000

1925 7.1 Yunnam, China 6,500 1963 6.0 Skoplje,

Yugoslavia

1,200

1927 7.5 Kitatango, Japan 2,925 1964 8.4 Prince William

Sound, USA

131

1929 7.1 Iran - former

USSR border

3,253 1964 7.5 Niigata, Japan 26

1931 7.9 Hawke's Bay,

New Zealand

1965 6.5 Caracas,

Venezuela

266

1933 8.3 Sanriku, Japan 3,008 1968 7.9 Tokachi-Oki,

Japan

49

1939 8.0 Erzincan, Turkey 23,000 1968 7.4 Iran 11,000

1940 7.1 Imperial Valley,

USA

8 1970 7.6 Peru 70,000

1940 7.4 Vrancea,

Romania

1,000 1971 6.5 San Fernando,

USA

65

1943 7.4 Tottori, Japan 1,083 1972 6.2 Nicaragua 5,000

1944 8.0 Tonankai, Japan 998 1976 7.5 Guatemala 23,0001944 7.4 Turkey 4,000 1976 7.6 Tangshan, China 650,000

1945 7.1 Mikawa, Japan 1,961 1976 7.3 Iran-USSR-

Turkey borders

5,000

1946 8.1 Nankaido, Japan 1,432 1976 6.5 Fruili, Italy 968

1948 7.3 Fukui, Japan 3,895 1977 7.2 Vrancea,

Romania

2,000

1949 7.1 Olimpia, USA 8 1978 7.4 Miyagiken-Oki,Japan

27

1950 8.6 India 574 1994 6.7 Northridge, USA 61

1952 7.7 Kern County,

USA

12 1995 7.2 Kobe, Japan 6055

Three main layers are composing the continental crust: a 15 20 km thicksediment

layer, a 5 20 km thick granite layer, and a 10 40 km thick basaltic layer. The

oceanic crust has a basaltic structure and is primary composed from Silicon andMagnesium, being named SIMA. Its density varies from 2.9 to 3.0 g/cm

3. It is thinner

than the continental crust, even from 5 20 km.

The crust plus some of the upper part of the mantle is divided in plates. These

plates are floating on the mantle, moving, determining the continental drift, and

generating the majority of the strong earthquakes.

As a second major internal sphere of the Earth, the mantle has a superior 900

km and an inferior 2000 km part. The superior part has a structure similar to the

oceanic crust.


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Figure 1.1 Internal structure of the Earth

2900km

3500km

5 60km

Crust

Mantle

Outer core

Inner core

Mohorovicic

discontinuity

The superior mantle has a lower layer with a mainly viscous consistency, called the

athenosphere. The crust and the upper mantle form lithosphere and have a thicknessof about 70 km. The athenosphere is located under the lithosphere until 400 km depth.

Table 1.2 Geologic history of the Earth

Precambrian Era

EracProterozoi

EraArcheozoic

Paleozoic Era

(242-564 Ma)

PeriodPermianPeriodousCarbonifer

PeriodDevonian

Period(Silurian)Gotlandian

PeriodOrdovician

PeriodCambrian

amphibia)of(Era

fishes)of(Era

s)trilobiteof(Era

Mesozoic Era

(64-242 Ma)

PeriodCretaceous

PeriodJurassic

PeriodTriassic

reptiles)of(Era

Cenozoic Era

(0-64 Ma)

Ma)1.7-(0PeriodQuaternary

Ma)64-(1.7PeriodTertiary

EpochAluvial

EpochDiluvial

EpochNeocene

EpochPaleocene

AgePliocene

AgeMiocene

AgeOligocene

AgeEocene

AgePaleocene

The core of the Earth is less known than the other parts of the Earth's structure. From

the measurements it was deduced that the inner core is solid, made mainly from iron,

while the outer core must be liquid. The density of material the in the Earth's core

might be about 17.65 g/cm3, while the temperature could be at around 6000 C at

millions of atmospheres pressure.

1.3 SEISMIC AREAS


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The Earth's crust is divided into some very large tectonic plates, see Figure 1.2:

Pacific plate, Eurasian plate, Philippine plate, African plate, Antarctic plane, Indian

Australian plate, North American plate, South American plate. Together with these

large plates, there are many other smaller plates as: Caribbean plate, Arabian plate,

Juan de Fuca plate, Cocos plate, etc.

Figure 1.2Main tectonic plates

70 N

50 N

30 N

10 N

10 S

30 S

120 W

PACIFIC

PLATE

NORTH

AMERICAN

PLATE

ANTARCTIC PLATE ANTARCTIC PLATE

NAZCA

PLATE

SOUTHAMERICAN

PLATE

AFRICAN

PLATE

EURASIAN

PLATE

INDIANAUSTRALIAN

PLATE

PILIPPINEPLATE

60 W 0 60 E 120 E

50 S

The movement of the plates generates the changing in the relief configuration and

leads to earthquakes at the fault lines. New faults can appear while others become

active or inactive.

1.4 CAUSES OF EARTHQUAKES

Major causes of earthquakes might be classified as it follows from Figure 1.3.- volcanoes

endogenous- tectonics- fall of underground cavities

- impact with meteorites- sudden changes of atmosphericpressure

natural

exogenous

- influences from other planets,

Sun, Moon, etc.- useful explosions- destructive explosionsblasts

- accidents- collapse of mines

- fall of underground cavitiesdue to extraction of water, oil,gas, etc.

Causes ofearthquakes

artificial

other, i.e.

- construction of dams

Figure 1.3 Causes of earthquakes

Tectonic earthquakes are phenomena of strong vibrations occurring on the ground due

to release of a large amount of energy, within a short period of time through a sudden

disturbance in the Earth's crust or in the upper part of the mantle. They amount more

than 90% of the total number of the earthquakes. Figure 1.4 is showing how the

tectonic plates are developing. Such phenomenon is in progress in Pacific Ocean.


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Figure 1.4 Plate tectonics

mid-oceanic ridge

mesosphere

plate (lithosphere)plate (lithosphere)

trench

island arc

volcaniczone

marginal

sea

continent

athenosphere

The process in which a plate is moving against and under another plate is named

subduction. During this process, because of the compressing that takes place, many

shallow or deep earthquakes are generated as shown in Figure 1.5.

Figure 1.5 Model of subduction zone

0 70 kmshallow earthquakes

300 600 kmdeep earthquakes

hypocenters

subduction zone plateplate

The place where an earthquake is generated is named hypocenter or focus.

Corresponding to the hypocenter, the projection on the external part of the crust (thevertical of the hypocenter) is named epicenter.

a) normal fault b) reverse fault

c) right lateral fault d) left lateral fault

Figure 1.6 Types of fault displacement


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1.5 EARTHQUAKE MECHANISM

As a result of plate tectonics the geological structures show ruptures caused by strain

beyond the deformational capacity. The ruptures are followed by sliding motions

between the opposite sides and create what is called geological faults.

Figure 1.6 shows the type of faults. A normal fault (Figure 1.6a) is showingmainly a tensile stress state and a reverse fault (Figure 1.6b) is generated by

compression. It is possible that the movement to be lateral, as presented in Figure 1.6c

and Figure 1.6d.

Fault line

c) compression

and tensile forces

d) double couple

a) before slip b) after slip

Figure 1.7 Earthquake mechanism due to fault slip

In Figure 1.7 a plan view of the area around a fault line is shown. Before the slip of

the fault (Figure 1.7a), the accumulation of energy is proved by the strain. The forces

and couples are released creating the fault and earthquakes.

For clarifying what happens after an earthquake in the neighborhood of a fault,

Figure 1.8 shows the situation of a road constructed after the straining.It is observed that there is an elastic rebound of the soil around the fault and

this determines the shape of the road after the earthquake.

Figure 1.8 Elastic-rebound theory mechanism

Fault lineDirection

of motion

Directionof motion

Road Road

a) before straining b) strained (before earthquake) c) after earthquake

1.6 SEISMIC WAVES

Earthquake energy is dissipated from the hypocenter through seismic waves. Deep

into the earth the seismic waves are identified of two major types: P waves (or

primary waves) and S waves (or secondary waves).


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As it is seen from Figure 1.9, a movement of material particles along the wave

propagation inducing alternative tension and compression deformations characterizes

the P waves. P waves produce volume modification of the layers they cross. These

waves have the highest velocity in their travel, being based on normal stress. They

arrive first in any earthquake surface area.

P-wavecompression

dilatation

S-wave

wavelength

Love wave

Rayleigh wave

Figure 1.9 Ground motion for different types of seismic waves

The propagation velocity of the P waves varies from 5 to 7 km/s and can be calculated

with the next equation

)21)(1(

)1(EVP (1.1)


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where: E is the Young's modulus, is the mass density of the soil, and is the

Poisson ratio.

In the case ofSwaves the movement of material particles is perpendicular tothe propagation direction, creating shear deformations, see Figure 1.8. Because of the

shear stress they create, the Swaves are felt later on the earth surface and they do not

modify the density of the material involved into the movement. Velocity ofSwavesmay vary from 3 to 4 km/s and Equation (1.2) gives the calculation formula

)1(2

EGVS (1.2)

where G is the shear modulus.

Because of discontinuities inside the Earth, two other different types of

seismic waves are observed: Love waves and Rayleigh waves. These waves are

propagating near the surface of the Earth. As a general notice it might be said that

Rayleigh waves correspond to P waves generation tension/compression stresses but

their amplitudes are decreasing with the depth. Similarly, Love waves arecorresponding to the Swaves, generating shear stresses decreasing with the depth.

It should be observed that there are other types of waves created by reflection

and refraction of the main type of waves and by their combinations.

Based on Equations (1.1), (1.2), and on measurements from at least three

observation points, the position of the focus and of the epicenter can be deduced.

1.7 EARTHQUAKE MEASUREMENT

Measurement of the earthquakes is very useful for getting knowledge about the

structure of the Earth. The main instrument used in earthquake measurement is theseismograph. From the seismograph's record, the earth movement is theoretically

calculated.

Figure 1.10 Principle of the seismograph

paper

advancing

direction of

vibration

damper

mass

In principle, a seismograph is composed from a mass with oscillations recorded on

paper, Figure 1.10.

The earthquake is shaking the seismograph's mass and the recorded line is

showing the intensity of the seismic activity. Because the dynamic characteristics ofthe seismograph are influencing the record, it can be easily understand that the range


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of availability of a record is limited. Therefore some seismograph will better record

accelerations (for short natural periods of the seismograph), or velocities, or

displacements (for long natural periods of the seismograph). Some seismographs will

be more suitable for weaker earthquakes and other will reflect more accurately

stronger earthquakes.

Figure 1.11 Kobe 1995 earthquake, NS acceleration record

0 10 20 30 40 50 60

-800

-600

-400

-200

0

200

400

600

KOBE NS 1995

818 gal

acceleration(gal)

time (s)

Figure 1.11 is showing the recorded accelerations, the North-South component, for

the earthquake from January 1995, in Kobe, Japan. The time with large peaks is

relatively short. However, the peak ground acceleration (PGA) is the largest ever

known, 818 gal (cm/s2), almost 1 g (9.81 m/s

2). Of course this large value is

questioning if the recording is proper or not.

1.8 SEISMIC SCALES

Because earthquakes are so complex and almost unpredictable phenomena, many

scales were proposed for measuring earthquakes.

An intensity scale is a scale for measuring the seismic intensity based on

human feelings and by the effects the ground motion has on structures or living

beings.

In 1564, Gastaldi proposed an intensity scale, followed by Pignafaro (1783). A10 grade intensity scale is the Rossi-Forel Scale (1883). Another scale is the Mercalli-

Cancani-Sieberg Scale, based on proposals of Mercalli (1902) and Cancani (1904). F.

Neumann (1931) did modifications on this scale. This 12-grade scale, Modified

Mercalli (MM) Scale, is largely adopted today, see Table 1.3.

The Medvedev-Sponheur-Karnik (MSK) scale is also a 12-grade seismic

intensity scale, proposed in 1964. The Japanese Meteorological Agency (JMA) is

using an 8-grade scale.

Figure 1.12 shows the equivalence between the three seismic intensity scales

(MM, MSK, JMA) and an approximation for the maximum recorded acceleration.

One of the most used based on measurements scale is the Magnitude Scale, or

Richter Scale. Charles Richter proposed it in 1935. The Richter Scale is defined as the

(base 10) logarithm of the maximum amplitude, measured in micrometers (10-6

m) of


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the earthquake record obtained by a horizontal Wood-Anderson seismograph with

magnification 2800, the natural period T = 0.8 s, damping coefficient 0.8, and

corrected to a distance of 100 km. The next equation shows the way the magnitude is

calculated

AM10

log (1.3)

whereA is the trace amplitude in microns, for an epicentral distance of 100 km.

Table 1.3 Abbreviated description of the Modified Mercalli intensity

Intensity Description

I Not felt except by a very few under especially favorable conditions.II Felt only by a few persons at rest, especially on upper floors of buildings. Delicately

suspended objects may swing

III Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many

people do not recognize it as an earthquake. Standing motor cars may rock slightly.

Vibration similar to the passing of a truck. Duration estimated.IV Felt indoors by many, outdoors by few during the day. At night, some awakened.

Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavytruck striking building. Standing motor cars rocked noticeably.

V Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable

objects overturned. Pendulum clocks may stop

VI Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen

plaster. Damage slight.

VII Damage negligible in buildings of good design and construction; slight to moderate in

well-built ordinary structures; considerable damage in poorly built or badly designed

structures; some chimneys broken.

VIII Damage slight in specially designed structures; considerable damage in ordinary

substantial buildings with partial collapse. Damage great in poorly built structures.Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture

overturned

IX Damage considerable in specially designed structures; well-designed frame structuresthrown out of plumb. Damage great in substantial buildings, with partial collapse.

Buildings shifted off foundations.

X Some well-built wooden structures destroyed; most masonry and frame structures

destroyed with foundations. Rails bent.

XI Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent

greatly.

XII Damage total. Lines of sight and level are distorted. Objects thrown into the air.

The magnitude is directly linked to the energy in the focus by Equation (1.4).

ME 5.18.11log10 (1.4)

where E is energy and M is the magnitude. As a consequence, an increase inmagnitude with one unit means an increase by a factor 32 for the energy, and an

increase with only 0.2 of the magnitude means a double energy.

An other way to measure an earthquake is the seismic moment, see Figures

1.6c and 1.6d. The seismic moment is produced by the couple of forces that appear

when a fault slips. Between the Richter magnitude, M, and the seismic moment, m,

the next equation was established:

Mm 5.11.16log10 (1.5)

The Spectral Intensity Scale, proposed by Housner, and the Spectral Action Scale,

proposed by Medvedev, are two other scales in use.

When describing an earthquake, the seismic scales are giving only a generalimage of it. There are many other aspects that must be taken into consideration. The


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measurements may refer to time domain or frequency domain characteristics. As an

example, in Figure 1.13 the Fast Fourier Transform (FFT) of El-Centro NS 1943

earthquake acceleration record is presented. It shows that peaks of frequency

components for this earthquake are concentrated in the range 1 2.5 Hz.

Figure 1.12 Equivalence between different seismic scales

MM 0 I II III IV V VI VII VIII IX X XI XII

MSK I II III IV V VI VII VIII IX X XI XII

JMA 0 I II III IV V VI VII

PGA 0.5 1 2 5 10 20 50 100 200 500 1000 cm/s2

A frequency analysis of an earthquake shows what is the range of frequencies that are

most influenced by the seismic activity. If the natural frequency of a building is

closed to high peaks in the frequency diagrams of an earthquake then high structural

response it is expected.

0 2 4 6 8 100

20

40

60

80

100

120

140

160

180

Frequency (Hz)

FFTamplitude

El-Centro NS 1940

Figure 1.13FFT of El-Centro NS 1943 earthquake acceleration record

The total time duration of an earthquake is showing important aspects. A very short

duration of an earthquake might represent a concentration of the earthquake energy. A

high number of zero crossings for the acceleration, velocity, and displacement record

is also a measure of the damaging potential of an earthquake. Especially the number

of the high-value peaks in the records is relevant for judging an earthquake.


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1.9 MAJOR ROMANIAN EARTHQUAKES. SEISMIC ZONATION

Romania is a seismic area with relative frequent strong earth shakings. Table 1.4

presents the major known Romanian earthquakes starting from 15th

Century, along

with their estimated or measured magnitude (Richter), M, and epicentral intensity

(MM),I0. Location of Romania is on the large Eurasian tectonic plate. This plate in itsSouth-West part collided with the African plate and determined the chain of

mountains in Europe: the Alps, Carpathians, and Caucasus.

While the North-West of Europe is almost seismic inactive, Romanian area is

dramatically marked by the Carpathians curved shape, especially the area named

Vrancea. In Vrancea the faults are active, with a return period estimated from 15 to 30

years for a strong earthquake. However, the number of felt and measured earthquakes

is much larger, 300 to 400 every year.

0 10 20 30 40

-200

-100

0

100

200

195 cm/s2

Acceleration(cm/s2)

Time (s)

Vrancea NS, March 4, 1977

Figure 1.14 Acceleration record of Vrancea NS, March 4, 1977 Romanian Earthquake

The studies done for the Vrancea seismic area led to an approximate relation between

the magnitude (M) and the epicentral intensity (I0) of the earthquakes, as in Equation

(1.6).

18.256.0 0IM (1.6)

The earthquake from 1940, November 10th

, made many victims (more than 1000, but

the real figure is not known). Bucharest, the capital of Romania, and other towns

(Galai, Focani, Panciu, Mreti, etc.) were very affected. In central Bucharest the

reinforced concrete made, 12 stories and 45 m tall, "Carlton" building collapsed. 136

people died under the ruin and the fire started immediately after the earthquake.

Another bitter lesson from the history of the earthquakes was that from March

4th

, 1977, see Figure 1.14. It was considered the strongest earthquake felt in Europe.

The shakings were felt even at Moscow, 1500 km from Vrancea, the epicenter's

location. Important damages had been recorded in many counties of Romania: Buzau,

Dolj, Iai, Ilfov, Prahova, Rmnicu-Srat, Putna, Teleorman, Vaslui.In Bucharest, 33 multi-story buildings, built before the Second World War II,

were destroyed during the 1977 earthquake. The true number of deaths is not reallyknown, but it is believed that more than 3000 people died. Injured people were more


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than 11000. The number of lost houses was more than 32000 and many other social,

cultural, industrial, agricultural, historical, and governmental buildings had been

damaged. The transportation's infrastructure, industrial equipment, and many others

were severe damaged.

Figure 1.15 Seismic zonation of Romania

After the 1977, March 4th

, the Earthquake Engineering in Romania was strongly

developed. The field was introduced as a compulsory independent course in all Civil

Engineering education. One of the most active people, a real pioneer of the domain,

was Professor Alexandru Negoi, who was the first to teach Earthquake Engineeringin the Faculty of Civil Engineering and Architecture of Iai.

Also, after 1977, the Earthquake Engineering Romanian Code, the P-100

Code, was issued and this led to an important increase in safety and quality of building

in Romania. The observation, measurement, and study of earthquakes in Romania

have become more and more enlarged since then. For every Civil Engineer inRomania, the knowledge of the Earthquake Engineering is a must.

As a result of the intensive studies, seismic countries are establishing the

seismic risk for each area. Figure 1.15 is showing the maximum probable earthquake

measured on MSK scale with a return period of 50 and 100 years for Romania. The

map from Figure 1.15 confirms that the Vrancea area is the most seismic area and an

earthquake with the intensity 9 on MSK scale is probable to occur once every 100

years.


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Table 1.4Major Romanian earthquakes

Date TimeEpicenter Depth

(km)M I0

Latitude Longitude

Aug 29 1471 10: 45.7 26.6 7.4 8

Aug 29 1473 45.6 25.4 6.4 8Nov 24 1516 12: 45.7 26.6 7.2 9

Jun 9 1523 45.7 26.6 6.1 7

Jul 19 1545 08: 45.7 26.6 6.7 8

Aug 17 1569 05: 45.7 26.6 6.7 8

Aug 10 1590 20: 45.7 26.6 6.9 9

May 3 1604 03: 45.7 26.6 6.7 8

Dec 24 1605 15: 45.7 26.6 6.7 8

Jan 13 1606 01: 45.7 26.6 6.4 8

Nov 8 1620 13: 45.7 26.6 6.9 9

Feb 1 1637 02: 45.7 26.6 6.4 8

Aug 9 1679 01: 45.7 26.6 6.7 8

Aug 18 1681 00: 45.7 26.6 6.7 8

Jun 12 1701 01: 45.7 26.6 6.4 8

Oct 11 1711 01: 45.7 26.6 6.1 7

Jun 11 1738 10: 45.7 26.6 6.9 9

Apr 16 1790 19: 45.7 26.6 6.7 8

Oct 26 1802 10:55 45.7 26.6 7.5 9

Nov 26 1829 01:40 45.7 26.6 6.4 8

Jan 23 1838 18:45 45.7 26.6 6.7 8

Dec 25 1880 14:30 45.7 26.6 6.1 7

Aug 17 1893 14:35 45.7 26.6 5.7 7

Sep 10 1893 03:40 45.7 26.6 5.7 7

Aug 31 1894 12:20 45.7 26.6 6.1 7Mar 11 1896 23:00 45.7 26.6 5.5 7

Oct 6 1908 21:40 45.5 26.5 125 6.8 8

May 25 1912 18:02 45.7 27.2 90 6.4 7

May 25 1912 20:15 45.7 27.2 100 5.8 6

Apr 18 1919 06:20 47.7 27.2 100 5.7 6

Aug 9 1919 14:38 45.7 26.6 120 5.6 6

Mar 30 1928 09:38 45.9 26.5 120 5.6 6

May 20 1929 12:17 45.8 26.5 100 5.6 6

Nov 1 1929 06:57 45.9 26.5 160 6.6 7

Mar 29 1934 20:06 45.8 26.5 90 6.9 8

Sep 5 1939 06:02 45.9 26.7 120 6.1 6

Oct 22 1940 90:37 45.9 26.4 125 6.2 7Nov 10 1940 01:39 45.9 26.7 135 7.3 9

Mar 12 1945 20:51 45.6 26.4 125 5.8 6

Sep 7 1945 15:48 45.9 26.5 80 6.5 8

Dec 9 1945 06:08 45.7 26.8 80 6.2 7

Mai 29 1948 04:48 45.8 26.5 130 6.0 7

Oct 1 1976 17:50 45.8 26.5 140 5.5 6

Mar 4 1977 21:22 45.8 26.7 110 7.2 9

Aug 31 1986 00:28 45.5 26.5 131 6.9 7

May 30 1990 13:40 45.8 26.9 91 6.7 8

May 31 1990 03:18 45.8 26.9 79 6.1 7

Documents

Seismology for Civil Engineers