Paper No.TS-3-2

FUNDAMENTALS OF THE EFFECTS OF EARTHQUAKES ON THE
GROUND AND STRUCTURES
Abel ORDOÑEZ1
SUMMARY
Important mining projects are being developed in our country, which require a structural design not only
for their buildings, process plants and various facilities, but also for their earth and mining waste
structures, where the concepts of performance-based seismic design of structures are being implemented.
The effects of an earthquake on the ground and on structures are based on the existing knowledge ofseismology, geotechnics, geophysics, soils dynamics and structural behavior. To the author, it is clear that
this is the current situation in many countries. The inertial model which aims at estimating seismic
forces, the basis of structural design, has been questioned in the past few years since the way it represents
the behavior of structures during an earthquake seems to be very limited, particularly when the structure
collapses on soft soil, where damages increase significantly causing sometimes large numbers of victims.
The work submitted herein is founded on the study of ground motion during an earthquake, considering
not only the acceleration but also the displacements generated by the earthquake. Two case studies arepresented based on experience acquired in the past years in the mining industry and alternative, different
structure failure mechanisms are proposed with a recommendation to review and complement the current
seismic design concepts.
INTRODUCTION
Performance of the foundation soil and soil structures under seismic loads has been discussed since 1987
by the International Society of Soils Mechanics and Geotechnical Engineering (ISSMGE) and its recent
contributions were summarized during the last International Conference of Performance-Based Design inGeotechnical Earthquake Engineering, Kokusho [1].The knowledge of ground motion and deformations
induced by an earthquake is the most important stage of performance-based design, particularly for soft
soil. A quick review of the ground motion and structure performance during the earthquakes that occurredin the world indicates that structures under a conventional seismic design are incapable of withstandinglarge deformations, especially when founded on soft soil, figure 1 and 2. Performance-based design isbased on the criterion of the tolerable ground motion in accordance with the structures’ design criteria andthe application of appropriate methodologies to determine them.
Ground Motion Caused by an Earthquake
According to Newmark [2], the effect of an earthquake on structures, the following should beconsidered:a) All of the earthquake’s characteristics, being the peak acceleration not necessarily the main factor ofseismic response.

1 National University of Engineering, Lima-Perú Email: ohabel@yahoo.com

Figure 1, 2: Evidence of excessive displacement on very superficial concrete slab foundation (the design
was based on the inertial model and horizontal force of the Peruvian Technical Standard E0.30 for
Earthquake Resistant Design, and did not consider the effect of the horizontal and vertical displacements
during the earthquake). Earthquake 8.15.07 in Pisco, Peru.

b) The effect of the earthquake’s velocity, displacement and duration may be of equal or greater
importance to determine the seismic response.
c) All of the earthquake’s characteristics, being the peak acceleration not necessarily the main factor ofseismic response.
d) The effect of the earthquake’s velocity, displacement and duration may be of equal or greater
importance to determine the seismic response.
Velocity (cinematic energy) is the most important variable to study motion as well as displacement(potential energy). Both are indicators of the intensity of the earthquake and therefore of potential damage
to structures. During the occurrence of an earthquake and the resulting ground motion, there are moments
during which the velocity is zero and there is maximum displacement. The earthquake’s intensity (energy)
should be assessed compared with its maximum velocity or maximum displacement (Fig. 3). From thisviewpoint, acceleration is not representative of the earthquake’s intensity (energy) and can therefore notnecessarily be the basis for the seismic design of the structures.
It should be highlighted that large accelerations recorded in recent earthquakes did not necessarily result inlarge structural or geotechnical damage. For instance, Kokusho [3] indicated that during the earthquakes
in San Fernando (1971) and Northridge (1994) in the USA, the peak ground accelerations (PGA) of
1.0G and 1.8G did not cause major structural damage in the surrounding areas. During the 2004
earthquake in Nigata, Japan, the 1.7G acceleration in Tokamachi did not cause the major damage as had
been anticipated either, and many similar cases have been recorded. This indicates that acceleration may
not be a parameter governing damage to structures, compared to other parameters such as displacement orvelocity, as Kokusho stresses [3].
The inertial model has its origin in the rigid body mechanics and is intended to estimate seismic forces in
the current design methods which are earthquake resistant; this is why it has been questioned in recent
years, Villarreal [5], as it is said to represent the behavior of structures during an earthquake in a very
limited way, particularly on soft soil.
The study of ground motion caused by an earthquake, where seismic waves experience the phenomenonof amplification in passing from bedrock to less dense soil, indicates the following:a) The energy which is generated by the earthquake and which propagates through seismic waves, does
so through elasto-plastic behavior.

b)
c)
d)

e)

The (non-recoverable) inelastic deformation component is the dissipated seismic energy, which iscalled ground damping.
Softer, less dense soils dissipate larger amounts of energy since they suffer larger unrecoverable
deformations than hard soils.
The energy is transmitted more slowly in soft soils compared to hard soil. Superficial seismic waves
in soft soil, for example, can travel at velocities between 50 and 200 m/s, while in hard rock they
propagate at a velocity exceeding 2000 m/s, which is 10-40 times faster.
The impedance of the physical medium associated with the difference in density between soil andbedrock transforms the bedrock’s kinematic type energy into energy of the potentially soft soil
deforming type.

Seismic Ground Amplification
The analytic methods used to study seismic amplification of the site in order to rigorously evaluate theeffect of an earthquake consider the following stages:
1) Establishment of an appropriate time-history record of bedrock accelerations to model the dynamic
response.
2) Modeling of the unidimensional dynamic response using the results of the previous stage andapplying dynamic modeling using the SHAKE program, Schnabel [4].
Time-History Record of Accelerations in Bedrock
The records used resulted from the processing records from 17 earthquakes occurred in Peru (Table 1).
From the assessment performed, processed records of seismic behavior accelerations in the country wereobtained. Based on the assessment of the predominant period, 06 records were selected as representativeof the subduction and continental sources seismicity (Table 2).
Unidimensional Dynamic Response ModelingIn the unidimensional dynamic analysis model, it is assumed that earthquake accelerations will occur inthe bedrock, making up a unidimensional ground column. From the bedrock, horizontal shear waves
propagate vertically and reflect on the deposit surface. The dynamic properties of the materials that makeup the profile were estimated from the results of measurement tests of surface shear waves, Vs, JapaneseSociety of Civil Engineers [5], Kramer [6] and Towhata [7]. Dynamic properties, such as shear modulus
and damping, were estimated from the existing technical literature (Hardin, 1972; Seed and Idriss, 1970;
Seed et al., 1984; Vucetic and Dobry, 1991).
Dynamic Parameters
The dynamic behavior was assessed unidimensionally through geophysical profiles, which have provided
average values for surface shear wave velocities Vs(30), in accordance with the IBC. Measurements ofvelocity profiles for surface shear waves were made through multichannel analysis of surface waves(MASW) Park et al., 1999; Xia et al. 1999; Miller et al., 1999.
Case 1: The effect of an earthquake on gravel soil
The soil is composed of gravel silty (GM, GW-GM, GP-GM and SM) with angular to sub-angularparticles and 4” - 7” diameter blocks. S.P.T. tests ranged from 10 to 35. Density varies from loose to
medium dense up to a depth greater than 50 meters. Four (04) geophysical profiles were evaluatedresulting in average surface shear wave velocity values Vs(30) of 340, 380, 400, 440 and 780 m/s
respectively. The seismic response analysis was carried out using the short period accelerations record(0.1 to 1 sec.) and long period accelerations (up to 1 and 3 sec) of the Pisco earthquake (2007) and
Yurimaguas earthquake (2005), respectively; the accelerations record was scaled to 0.22 g. The results ofthe seismic amplification analysis at ground surface level are shown in Tables 3 and 4.

2

Amax=200cm /s (T=0.2-0.5seg)
Registro de Aceleración - Sismo de Pisco 100-110 seg
0.25
0.20

Acceleration (g)

0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
100

101

102

Vmax=30cm/s (T=1-1.5seg)

103

104

105

106

107

108

109

110

107

108

109

110

107

108

109

110

Time (sec)Registro de Velocidad - Sismo de Pisco 100-110 seg

40
30

Velocity (cm/sec)

20
10
0
-10
-20
-30
-40
100

101

102

103

104

105

106

Time (sec)

Dmax=15cm (T=2-4seg)

Registro de Desplazamiento - Sismo de Pisco 100-110 seg
15

Displacement (cm)

10

5

0

-5

-10

-15
100

101

102

103

104

105

106

Time (sec)Figure 3: Acceleration, velocity and maximum displacement (by integration in surface soft soil), during
the 10 most intense seconds (100-110) of the Earthquake 8.15.07 in Pisco.

Station

Table 1: Calibrated and Evaluated Earthquake Records
Earthquake
Date
Magnitude
StrikeU.N.S.A. Arequipa
Tarapacá
Characato-Arequipa
Tarapacá
Characato-Arequipa
Pisco
CallaoPisco
C.D. Lima-CIP
Pisco
CISMID-UNI
Yurimaguas
CISMID-UNI
Pisco
La Molina-Lima
Yurimaguas
La Molina-Lima
Pisco
G.R. Moquegua
Arequipa
G.R. Moquegua
TarapacáMoquegua
TarapacáMoquegua
Tarapacá
Moyobamba-San Martín Yurimaguas
U.N. Jorge Basadre-Tacna Arequipa
U.N. Jorge Basadre-Tacna Tarapacá
U. Privada Tacna
TarapacáJun-13-05
ML=7.2, Mw=7.8
Jun-13-05
ML=7.2, Mw=7.8
Aug-15-07 ML=7.0, Ms=7.9, Mw= 8
Aug-15-07 ML=7.0, Ms=7.9, Mw= 8
Aug-15-07 ML=7.0, Ms=7.9, Mw=8
Sep-25-05
ML=7
Aug-15-07 ML=7.0, Ms=7.9, Mw=8
Sep-25-05
ML=7
Aug-15-07 ML=7.0, Ms=7.9, Mw=8
Jun-23-01
Mb=6.9, Mw=8.3
Jun-13-05
ML=7.2, Mw=7.8
Jun-13-05
ML=7.2, Mw=7.8
Jun-13-05
ML=7.2, Mw=7.8
Sep-25-05
ML=7
Jun-23-01
Jun-13-05
ML=7.2, Mw=7.8
Jun-13-05
ML=7.2, Mw=7.8

E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W

Table 2: Representative Earthquake Records
Earthquake (recorded)
acceleration
displacement
recorded
calculatedg
Tarapacá 2005 (Arequipa)
0.13
3.0
Pisco 2007 (Lima)
0.05
2.5
Arequipa 2001 (Moquegua)0.30
5.0
Tarapacá 2005 (Moquegua)
0.05
0.3
Yurimaguas 2005 (Moyobamba)
0.14
7.0
Tarapacá 2005 (Tacna)
0.12
2.8
Table 3: Case 1: Acceleration Amplification Factors
ProfileVs(30)
Pisco (2007) Yurimaguas (2005)
1
340
1.5
1.6
2
380
2.1
3.5
3
400
2.1
3.1
4
440
1.8
2.1
5
780
2.0
1.5
Table 4: Case 1: Displacement Amplification Factors
ProfileVs(30)
Pisco (2007) Yurimaguas (2005)
1
340
1.1
1.3
2
380
1.1
1.2
3
400
1.0
1.2
4
440
1.1
1.2
5
780
1.0
1.1

Dist.
Hypoc.
422
414
520
200
200
706
200
713
200
340
324
323
320
146
220
231
232

S. Fourier
period<0.1
0.3-1.5
0.4-1.0
0.1
0.3-4.0
0.2-0.5

Case 2: The effect of an earthquake on sandy soil
The soil is composed of sand and silt (SM, ML, SP-SM), of recent formation. S.P.T. tests ranged from 4
to 30. Density ranges from loose to medium dense to a depth greater than 30 meters; there is no groundwater table. Three (03) geophysical profiles were assessed which resulted in average surface shear wave
velocity values Vs(30) of 200, 240 and 270 m/s, respectively. The seismic response analysis was carriedout using the accelerations record of the earthquakes in Pisco and Yurimaguas; the acceleration record
was scaled at 0.40 g. Tables 5 and 6 shown he results of the seismic amplification analysis.
Table 5: Case 2: Acceleration Amplification Factors
ProfileVs(30)
Pisco (2007) Yurimaguas (2005)
6
200
1.1
1.1
7
240
1.4
1.6
8
270
1.8
1.7
Table 6: Case 2: Displacement Amplification Factors
ProfileVs(30)
Pisco (2007) Yurimaguas (2005)
6
200
1.3
2.0
7
240
1.3
2.2
8
270
1.2
2.0
The real case study of seismic wave propagation in the ground shows the following:a) The predominant vibration or seismic motion period of the ground is associated with the soil density
and rigidity.
b) The predominant vibration period of the bedrock ranges from 0.1 to 1 second. The predominantvibration period in soft soil may reach values from 1 to 3 seconds.
c) Energy damping or dissipation is larger in soft soils.
d) Degradation or reduction of rigidity in soft soil is very significant, reaching up to 10-20% of theinitial rigidity for 1% deformation.
e) Strong, short-period earthquakes (between 0.1 and 1 second) in hard soil cause accelerations above
1.0G, associated with the acceleration amplification phenomenon. Strong, long-period earthquakes(between 1 and 3 seconds) in soft soil cause deformations exceeding 1%, generating loss of rigidity,
loss of strength and excessive increase of displacements, from 10 to 25 cm, associated with thedisplacement amplification phenomenon due to the seismic resonance.
f) The inertial model cannot be applied to structure behavior in soft soil. Instead, ground displacement
should be considered during an earthquake, or a combination of both. In the proposed kinematic
model, apart from the inertial model, other failure mechanisms should be evaluated, wherehorizontal shear stresses are not necessarily dominant.
Seismic Amplification Study in Lima
According to Predes, an earthquake with a magnitude of Mw 8.0, similar to the one that occurred in
Pisco, with an acceleration of 0.35-0.40g, is expected to occur in Lima in the next years. In Table 7,
CISMID-UNI [8], proposes the following seismic amplification factors for accelerations, to be applied inaccordance with the earthquake resistant standard based on the inertial approach. In 2009, WAPMEER(World Agency for Planetary Monitoring and Earthquake Risk Reduction) made preliminary estimatesof losses due to possible earthquakes in Lima, and concluded that if 50% of the people are locatedinside buildings at the time of an earthquake, between 7,000 and 30,000 people will die. In the worst
case scenario, which is at night, with an 80% occupation of buildings, the number of fatalities would range
from 10,000 to 50,000, Predes [9].

Table 7: Seismic Amplification in Lima - CISMID-UNI (2003)
Seismic Amplification
Soil Type
FactorType I: Hard soil, old conglomerate, dense and consolidated.
1.0Type II: Intermediate soil, La Perla, San Miguel, La Molina,
1.2
Los Olivos, San Juan de Miraflores, Surco. Sandy and silty
sediments of limited thickness, less than 10 meters.
Type III: Soft soil, San Juan de Miraflores, Chorrillos, Callao,
1.4
Villa El Salvador, Magdalena. Sandy and silty soil with athickness greater than 10 meters.
Type IV: Very soft soil, Ventanilla, Chorrillos, San Juan de
1.4
Miraflores, Villa El Salvador. Coastal sand, loose sand withpresence of a ground water table.
For the aforementioned estimates, a magnitude 8 earthquake was used. An amplification factor for strong
ground motion was considered based on the CISMID-UNI microzoning map. The results of thesestudies suggest in the near future to review, complement the seismic microzoning studies, the earthquake
resistant methodologies, the Technical Standard for Soils and Foundations and for Earthquake Resistant
Design.
Failure Mechanism and Solutions Associated with the cinematic ModelIn the cinematic model, based on the movement induced by an earthquake in the structures, not only
horizontal, but also gravitational (vertical) forces are produced because it is made possible by the groundmotion. Moreover, it has been determined that horizontal acceleration in soft soil is controlled (decreased)by the impedance of the phenomenon of seismic wave propagation. The failure mechanism in soft soil isassociated with the gravitational forces that generate shear strengths in the vertical plane of any structure(Figure 4,5,6), associated with the vertical and slow undulating motion of the ground (for a large
predominantly long period). It is estimated that the vertical shear strengths will reach magnitudes which
are much greater than those currently estimated, based on the inertial model; therefore, there is still alarge amount of damage current engineering cannot control, unless special structures are used as in thecase of the Latin American Tower located in the soft zone of Mexico City. This is a 44 story building
founded on piles, which was built in 1956. It withstood the M=7.7 earthquake on July 28, 1957; theM=8.1 earthquake on September 19, 1985 and the M=7.9 earthquake on March 20, 2009. It is estimatedthat shear strengths in conventional structures are of such magnitude that other alternatives will besearched in order to reduce not only shear strengths through light and flexible structures, but also to
reduce the structure motion by replacing or reinforcing the foundation soil using non-conventional
materials such as geosynthetics, Tatsuoka [10] and The Japanese Geotechnical Society [11] orconsidering deeper foundations.

Figure 4: Damage caused by vertical displacements and excessive differentials in the ground during anearthquake.

Figure 5: Structure failure caused by vertical shear stress concentration.

Figure 6: Failure caused by turn over in structure founded on a surface concrete slab.
ACKNOWLEDGEMENTS
To Knight Piesold for to participate and to develop these studies in their most important mining projects,
and to OM Ingeniería y Laboratorio for their experience in performing MASW geophysical testing.
REFERENCES
Kokusho T., Tsukamoto Y., Yoshimine M. “Performance-Based Design in Earthquake GeotechnicalEngineering from Case History to Practice”. CRC Press, 2009.
2. Newmark, N.M. “Effects of the earthquakes on dams and embankments”. Geotechnique, Vol.15,
No. 2, page 139-160, 1965.
3. Kokusho T. “PDB in Earthquake Geotechinical Engineering and Energy-Based Design; Proceedingsof the International Conference on Performance-Based Design in Earthquake GeotechnicalEngineering”, 2009.
4. Schnabel P. B., Lysmer J., Seed H. B. “SHAKE: a computer program for earthquake response
analysis of horizontally layered sites”, University of California, 1972.
5. Japanese Society of Civil Engineers, “Dynamic Analysis and Earthquake Resistant Design”, Volume
3, Dams, Nuclear Power Plants, Electrical Transformers and Transmission Lines, Above ground
Storage Tanks and Piping. A.A. Balkema, 2001.
6. Kramer S.L. “Geotechnical Earthquake Engineering”, Prentice Hall, 1996.
7. Towhata I. “Geotechnical Earthquake Engineering”, Springer, 2008.
8. CISMID-UNI. “Estudio de Vulnerabilidad y Riesgo Sísmico en 42 distritos de Lima y Callao”,
CISMID/APESEG–EVR–LYC, 2004.
9. PREDES “Diseño de escenario sobre el gran impacto de un sismo de gran magnitud en Lima
Metropolitana y Callao, Perú”, 2009.
10. Tatsuoka F. “Recente practice and research of geosynthetic-reinforced earth structures in Japan”.
Tokyo University of Science, Japan, 2011.
11. The Japanese Geotechnical Society. “Geo-hazards during earthquakes and Mitigation measures”.
July 2011.
1.