Fundamental Investigation Concerning Restoration of Ruins of Machu Picchu: Discussions on Seismological Aspects

Fundamental investigation concerning restoration of ruins of Machu Picchu: discussions on seismological aspects

M. ~ujisawa'& K. sudo2 1 Tsukuba College of Techrzoloa, Japan 2 Institute of Industrial Science Urliversity of Tob.0, Japarl

Abstract

Machu Picchu is arguably the most famous ruins of the Incaic Empire. It is located northwest of Cuzco City. the former capital of the Incaic Empire, and southwest of Lima, the present capital of the Republic of Peru. This paper summarizes and discusses the results of site investigations, including seismological surveys. The site is being investigated by a Japanese mission comprised of experts from the fields of archeology, city planning, structural engineering, seismic engineering, seismology, geology and soil engineering. The results of the site investigations suggest the following; 1. There are two types of earthquakes that could inflict damage on Machu Picchu. The first type would originate from a wide, seismically active area that lies 100- 200km beneath the surface of Alequippa, about 100km to the south.

2. The second type would originate from one or more of the numerous activating faults that traverse the vicinity of the ruins. 3. The Zurite fault, which lies at the western end of the Cuzco active fault system, is only 35 km away, making it the closest fault to Machu Picchu

4. Although no destructive earthquakes have been known to occur in the vicinity of the ruins, there is a possibility that an earthquake of the 6.5 magnitude class could occur about 35km to the south, sometime in the future. 5. With the exception of two or three places, the ruins have remained stable, and they are not in immediate danger of collapse. However. since they are damp and located on steep mountain slopes, they might not be able to withstand a major earthquake sometime in the distant future.

1 12 Structural Studies. Repairs and ,2faintenance of Historical Buildings

1 Introduction

This paper reports on the results of surveys and analyses conducted on the preservation of the ruins at Machu Picchu, Peru, by a Japanese survey team that was dispatched to the site in 1990 at the behest of the Peruvian government. The team consisted of JICA specialists from the fields of archaeology, architectural planning, structural engineering, seismic engineering, seismology, geology, and soil engineering. Survey activities were conducted with the cooperation of the Peruvian Culture Agency (Cuzco office), National Polytechnic University, Japan-

Peru Earthquake Disaster Prevention Center and the Amano Museum. The main missions of the team were to develop fundamental measures for protecting the ruins from natural disaster, gain a thorough understanding of the state of the ruins, and collect relevant materials. Follow-up surveys were subsequently taken in

1995 and 1998, and the results of all surveys were used to create an analytical case study on seismic evaluations and proposals for the ruins.

2 Seismological Considerations

2.1 Seismic activity and potential seismic movement

2.1.1 Recent seismic activity Earthquakes with the potential for damaging the ruins of Machu Picchu can be categorized into two groups. The first group is found in an area of seismic activity about 100-200km below the ground surface in Arequipa, about lOOkm to the south of the ruins. This area is almost continuously active, with earthquakes exceeding 6 in magnitude occurring about once every 10 years. In an area under the northern Lake Titicaca region about 150km southeast of Cuzco, there are many of the world's deepest hypocenters. For example, see figs. 1 and 2, which depict the Magnitude 7.5 quakes that occurred in August and November, 1963. The type of damage that occurred at the epicenters (seismic occurrence mechanism) has been intensively studied by many researchers. Since the hypocenters were very deep, the quakes emitted P waves that were thrust almost directly upward from deep underground, and S waves that oscillated in a roughly

E-W direction. However, since almost no surface waves were generated, they were apparently slow, low-frequency waves, and it is believed that almost no long periodic (slow) oscillation occurred. Since the locations of earthquake occurrence are now known, it is possible to calculate the possibility of a hypothetical earthquake at the Machu Picchu site.

The second group is believed to be activated by numerous faults that traverse the vicinity of Machu Picchu. Since they are exeemely rare. they are not easy to find in the seismic activity maps based on the earthquake occurrence catalog compiled by the International Seismic Center (ISC). However, this type of information is the most important for predicting seismic damage at Machu Picchu, as will be discussed in detail in the next section.

&wetural Studies, Repairs and Maintenance of Histoma1 Buildings 1 13

Figure 1 Earthquake activity around the Republic of Peru (1985-1990)

This is a plot of earthquakes (mbx.0. n>10) using the ISC catalog. The numbers on the left refer to magnitude

Figure 2 Earthquake activity in the Cuzco area (1 985- 1990) Se~smicactiwty In the Cuzco area. The square shown by the arrow in the cenier of the figure de- picts the 50kmx50km central region. See Fig. ?for explanation of symbols

1 14 Structural Studies, Repairs and Maintenance of Historical Buildings

This means that the detailed surveys taken in the aftermath of the Magnitude 5.3 earthquake which struck the Cuzco area (epicenter 13.42 deg S, 71.81 deg W, according to ISC) on 5 April 1986 at 20:OO IJT (15:OO local time) may be of vital importance for predicting future quakes here. The Mercali intensity of this disastrous quake at Cuzco was revised to V-VI, with at least 16 people killed, 170 injured, and 2000 homes demolished. Materials include the detailed surveys and research of Dr. E. Deza of the IGP

(Geophysical Institute of Peru) and the surveys of peripheral damage conducted by the Cuzco office of the Peruvian Culture Agency (see References). Despite these efforts, however, the physical nature of this earthquake cannot be determined. The first impeding factor is the depth of the hypocenter. According to

ISC, it was 55+8krn below the surface (IGP says 57km), making it quite difficult to establish a relationship, as Dr. Deza did, with the Tambomachay fault that runs in an E-W direction north of Cuzco. According to IGP, it is somewhat odd for the depth of most of the aftershocks to have been determined to be about 10krn. More recently, Cabrera et al. (1989) revealed that during this quake (as will be discussed later), the Chincheros-Qoricocha fault generated displacement further to the north of the Tambomachay fault (Ref. 2). Therefore, this must be a shallow quake, so it should be reinvestigated. An earthquake research group from Harvard University (USA), using a so- called digital seismic observation net (GDSN), analyzed the records of the seismic waves. They found that the depth of the quake was 36k27krn with a scale of

7.7~10 dyne cm (MW= 5.2). As shown in Figs. 3-4a, b, c, the mechanism of the quake was a simple S-h' tensile-type normal fault running at an angle of 12ldeg, with an inclination of 32deg and slip angle of 65deg. This agrees with the geological and other theories that consider it to be the same type as the Tambomachay and Chincheros- Qoricocha faults. To estimate seismic inputs, it is important to know both the seismic record and the characteristics of the earthquake in question. To learn these characteristics, it is necessary to conduct regular seismic observations.

S QDA. QUISARM,AYO

Falla Qor~cocha F ai la ~ombomachay FM. S. SEBASTIAN C4P.1S ROJAS FM. YUNCAY?ATA

Figure 3 Surface faults (Deza. et al., 1986)

Structural (a) and seismlc (b,c) schemes of the Cuzco Earthquake (a) N-S structural cut between Lake Qorchocha and the city of Cuzco (b) Depth of the dislocation

Figure 4 Mechanism of the occurrence of the Cuzco earthquake (Dzlewonski, et al., 1987)

2.1.2 Seismotectonics In recent years in Peru, there has been much seismotectonic research about the relationship between active tectonics and this particular earthquake, especially in the Cuzco area (for example, Sebrier et al., 1985. 1988; Cabrera, 1987; Cabrera et al., 1987, 1988, 1989; Deza, 1986). According to these studies, the zone that forms the boundary between the Eastern Cordillera, which runs from the northern shore of Lake Titicaca NW through Cuzco then W to Ayacucho, and the High

Plateau, first became an active fault through crustal movements during the Quarternary (see Fig. 5). Along this zone, numerous destructive earthquakes have been recorded. The Cuzco Active Fault Group, which is relatively close to lMachu Picchu, is composed of several faults centered on Cuzco that run for about 120km in a discontinuous W-E line. From west to east, these faults include Zurite, Tamboray,Chincheros-Qoricocha, Tambomachay, Pachatusan. and Urcos. With the exception of the N-S Tamboray fault, all of them are E-W oriented normal faults that dip toward the south. During .the mb (short wavelength magnitude) 5.3 quake that hit the Cuzco area in April 1986, about a 3km stretch of the l0km-long Chincheros-Qoricocha fault (about I l km north of Cuzco) subsided l-lOcm with a dip toward the south, causing displacement of the normal fault. Cabrera et al.

(1989) revealed that for about 10,000 years B.P. (=1986), this fault had caused at least three earthquakes of Mw (moment magnitude) of 5.5-6.5.

11 6 Stnrcturai Studies, Repairs and Maintenance of Historical Buifdings

Structural sketch, drawn from satellite imagery and held observations, showing situation of the stud- led Chincheros-Qoricocha fault sector. l.ke caps 2.Quatemary basins 3.Mesozoic and Cenozoic formations of the High Plateaus 4.Paleozoic rocks of the Eastern Cordillera 5.Quatemary normal faults (hatchured on the side of the downthrown block) 6.Pre-Quaternary faults 7.anticlines 8.syncl1nes 9.flexures 10.sinistral strike-slip faults 1l.villages destroyed by historical shallow earthquakes 12. Epicenter, from USGS catalog and JGP data, of the May 21,1930 (M=6.0), May 8, 1965 (M=4.3), April 5, 1986 (mb =5.3) earthquakes.

Figure 5 Active fault systems in the vicinity of Machu Picchu

The closest member of the Cuzco fault group to Machu Picchu is the Zurite fault, on the western end. The straight-line distance from its western half to the ruins is a mere 35 kilometers. This 50km-long fault, which is the longest in the group, is segmented into several sub-faults at its eastern end, forming a half column pattern. At the southward-dipping normal fault, the vertical displacement in the central part of the Pleistocene Quarternary layer is 300 meters but not more than

100 meters in the upper part and a maximum 20 meters at the newest terrace (Cabrera et al.: 1987). Although the western half also appears to be divided into several segments, there is still not enough information to make a definitive conclusion.

Figure 5 indicates that there are almost no active faults west of the Zurite fault. However, some references, such as Sabrier et al. (1985), have speculated that several long faults might exist there, but the area has not been extensively surveyed.

According to Dr. E. Deza of IGP, there have been many damaging earthquakes of the Magnitude 5-6 class in Peru's interior, and the active faults are believed to be gradually destroying the crust, so the magnitude limit in the Cuzco area appears to be about 6.5. Cabrera et al. (1985) concluded that about 20km of the

Zurite fault was active, and postulated that it had the potential to generate a MW =

6.6-7.2 (mb 6.1-6.5) quake. The above information indicates that there have been no destructive earthquakes in the Machu Picchu area, but we should remember that an earthquake of the

Magnitude 6.5 class is predicted for this zone about 35 kilometers or so south of the site. It should also be noted that satellite photoimages have confirmed several lineaments near the ruins, but these have not appeared to be active faults. In the present survey, about 120 aerial photographs of the surrounding area (scale: 1:20,000) were obtained to identify and interpret lineaments, but as of this writing we have found no fault displacement patterns that would signify active faults.

Therefore, we believe that a shallow earthquake will not occur immediately under the ruins. Future issues in making seismic movement evaluations of the ruins will include 1) making a detailed survey of the active fault that is assumed to stretch from the western end of the prophase Zurite fault to Abancay, and 2) analyzing lineaments by interpreting aerial photographs of a 35km radius around the ruins.

2.1.3 Historical earthquakes There does not appear to be any historical evidence of damage to the Machu Picchu ruins sustained during earthquakes in and before the 19th Century, so damage must be inferred based on damage sustained at Cuzco. With the help of

IGP, Dr. A. Giesecke, Dr. Ceresis (the head of the South American Regional Earthquake Center) and others, as well as with the excellent and accurate earthquake catalog compiled by Konzo Miyamura, former professor at Tokyo University, we were able to piece together the history of seismic damage in that city and establish relationships with local faults. For example, it is possible that efforts to find new materials will result in a deeper understanding of the 1650 quake, which appears to have been the most disastrous one since the beginning of the colonial period.

2.2 Vibration characteristics of the foundation of the ruins

Table 1 Normal survey point

Site / Altitude l Date [Time /minute /Weather l Component (T- ~ernde of the condor / IOW 1 YOBIS/ l6 : 00 1 10 / ~inewindless / NS EW.UD I (2'Tern~leof the Sun middle 190/3,3 17 : 00 15 Fine. windless NSEWWD / / / / / lmtihautana I high /YOBIS108 : 30 / 10 /Fine.windles IN SEW.^

In the field of earthquake prediction, theories and methods have both rapidly advanced in recent years. Seismic movement is based upon three facets: 1) characteristics of the hypocenter (type of destruction that occurs underground during an earthquake), 2) the te~~ainon which structures are built, and 3) the

11 8 Stncctural Studies, Repairs and Maintenance of Historical Buildings

physical propel-ties of the geology underlying this terrain (underground structure). In order to know the underground structure? we used observation equipment from the Japan-Peru Earthquake Disaster Prevention Center (CISMID) to

continuously measure minute movements at three points on the foundation slope: 1) Condor Plaza, 2) The Temple of the Sun, and 3) Intiwatana. All of the measurements were taken on exposed granite in what were considered to be especially important historical structures (Fig. 6). Table 1 lists the specifications

of each observation.

s~teof ieligiaus Ma~nEntrance Temple cf the SJ~ '3 c?renanles

Buildings n the Mall iemp!e Stone err! nll ~l~eeragr':ultural area\$ Home of :he H~ghPilest AgricuI!ural area @ IntiraJtana

Figure .6 Observation points for minute seismic movements

The continuous measurements of minute movements were taken from three axes: N-S (north-south), E-W (east-west), and U-D (up-down). At the Temple of the Sun (Site 2, E-W), an especially long (about 5 seconds) oscillation was detected (Fig. 7). As Table 1 indicates, these measurements were taken under windless conditions, and the reason for this anomaly is still unclear. It might have originated from a special, non-wind vibration source, or maybe from the vibration characteristics of the site itself. To make a definitive conclusion, it would be best to take simultaneous measurements from several different sites. This would not only help us learn more about the long oscillation, it would also help us get a more accurate understanding of the seismic response at the entire Machu Picchu site. Figure 8 shows frequency analyses of the continuous record of minute movements. At sites 1 and 3, oscillation patterns are very sindar, with a proper

period of about 0.4 sec (2.5Hz). However, at site 2 there was very unusual behavior, with a proper period of about 0.25 sec (4Hz). For this site, it is necessary to analyze proper periods of the intrusive granite. Site 2 has the following two characteristics that are different from the other two sites: 1) It is located near a fracture zone that longitudinally runs (the length of) the ruins, and 2) there are caves, etc., in the granite. When reinforcing the structures on this site. it will be necessary to consider these differences.

Figure 7 Record of minute seismic movements (Sites 1,2and3,EW orientation)

" LL F requency (Ht) F requency(Hzj F reauency (Hz)

Figure 8 Fourier spectrum of record of minute seismic movements (EW orientation)

3 Summary of and Proposals for Survey Activities

The information reported in this paper indicate that, with two or three exceptions, the ruins are in a stable state of preservation, and we do not believe that there is any imminent danger of destruction. However, since the ruins are moist and on steep slopes, they might not be able to withstand a major seismic vibration that might occur sometime in the distant future. In order to preserve these ruins. among the most valuable cultural assets in the world, drastic measures will have to be implemented. As a first step, our survey group would like to propose that the following

1 20 Structural Studies, Repairs and Maintenance of Historical Buildings

surveys and observations be conducted in order to have an accurate understanding of the environment of the ruins.

3.1 Seismic observations

Here is no record of earthquake-induced damage in the area around the ruins, and the level of seismic activity there is believed to be lower than in Cuzco and other local areas. However, near an area about 35krn south of the ruins there appears to be a seismotectonic belt that extends from Cuzco: and there is a possibility that relatively frequent quakes might occur there. In addition, since the ruins are on the tail of a steep slope, there is a fear that seismic movements might occur that would be difficult to predict from flatland data. To learn about such seismic movement at Machu Picchu and seismic activity in the surrounding area, it would be ideal if we could set up an observation network consisting of observation points within the ruins and at least 3 points in the surrounding area. However, the reality is that a permanent observation point or points would first have to be set up within the ruins, followed by temporary (mobile) observation points in the surrounding area. Then work could proceed in stages on a full-scale observation network. At any rate, these observations would be essential for estimating the frequency of occurrence and associated values of seismic movement around the ruins.

3.2 Urgent need for detailed engineering surveys and evaluations at specific points

We propose the following urgent preservation measure based on detailed surveys made by seismic engineers: 1. Simultaneous, multi-point observations should be made of normal minute seismic movements in order to understand the dynamic characteristics of the entire ruin area.

4 Concluding Remarks

It would be preferable if a survey organization of the Peruvian government could undertake the above project, but it would be more realistic to think of a consortium of organizations from relevant countries, including Japan, working with the Peruvian government in this matter. Regarding the proposed surveys, there would be no changes in the current situation so there shouldn't be a problem if all countries decide to work together and Japan and Peru agree to it. However, it would be best if such a plan were carried out by first reaching international agreement on the types of observations and the duties and obligations of the countries involved. To achieve this goal, we would like to promote a close alliance between Japan and various organizations such as UNESCO for survey and research planning, and propose that Peru host an international conference for the purpose of establishing a master plan for the preservation of the Machu Picchu ruins.

Shuc~nlShcdres, Reparm and ,I.farntertanee ofHzstancal Burldings 12 1

References

Cabrera, J. :Estudios Neotectonicos en la region de Cuzco . la falla activa

de Qoricocha y su reactivacion durante el sismo del 5,4,1986. Informe I. G. P., 27. (1987). Cabrera, J., Sebrier, M. and Mercier, J. L. : Active normal faulting in High Plateaus of Central Andes . the Cuzco Region (Peru). Annales

Tectonicae, vol. 1, 116-138. (1987). Cabrera, J., Sebrier, M,, Deza, E. and Huaman. D. : An active and seismic normal fault sector in High Andes . the active Chincheros-

Qoricocha fault sector and its reactivation during the April 5, 1986 shallow earthquake (Cuzco Region Peru). 109-132.( 1989). Deza, E. La zona sismicamente activa del area de Cuzco con ocasion del temblor del 5 de Abril 1986. Informe I. G. P., 13 (1986).

Sebrier. M., Mercier, J.L., Megard. F., Laubacher, G. and Carey- Gailhardis, E. : Quaternary normal and reverse faulting and the state of stress in the Central Andes of South Peru. Tectonics, vol. 4, 739-780. (1985).

Sebrier, M,, Mercier, J. L., Machare, J., Bannot, D., Cabrera, J. and Blanc, J. L. : The state of stress in an overriding plate situated above a flat slab the Andes of Central Peru. Tectonics, vo1.7, 895-928. (1988).

Catalogo Sisrnico del Peru. 1500-1982. Instituto Geofisico del Peru. (1986). Cusco Sismo 86. Evaluacion de Inmuebles del Centro Historico Instituto Nacional de Cultura del Peru. (1986).

El Sismo del Cuzco del 5 de Abril 1986, Ernesto Deza. ( Estudio Sisimologico Instrumental, estudio de Intesidartes Locales y Regionales. Estudio Neotectonico) (1986)