TSUNAMI HAZARD ASSESSMENT FOR THE
CENTRAL COAST OF PERU USING NUMERICALSIMULATIONS FOR THE 1974, 1966 AND 1746
EARTHQUAKES
Sheila Yauri
MEE10521

Supervisor:

Yushiro FUJII 
Bunichiro SHIBAZAKIABSTRACT
A comprehensive study of tsunami simulation for the two recent events in 1974 (Mw8.0), 1966(Mw8.1) and one historical event in 1746 (Mw8.5-9.2) was carried out in order to constrain thetsunami source and evaluate the tsunami hazard in the central coast of Peru. We propose a seismic
source for each event in 1974 and 1966 and evaluate the tsunami heights and arrival time byperforming a tsunami simulation using a TUNAMI-N2 code that solves non-linear long wave
equation. Also, in order to reproduce the historical tsunami in 1746, we carried out a simulation for
scenarios with Mw of 8.5, 8.8, 9.0 and 9.2. Through a comparison among the historical tsunami
descriptions, the scenarios with Mw 8.8-9.0 were found to be more representatives, which is consistent
with the maximum tsunami heights observed from Huarmey to Barranco stations. Moreover, we adopt
a more realistic future tsunami scenario using a predicted slip model from an interseismic coupling
using GPS data provided by Pulido et al. (2011). This scenario shows an important coupling areafacing Huacho Lima and Pisco cities and according to the moment deficit a repetitive event of the1746 earthquake could occur. Also this model shows that the events in 1940, 1966, 1974 and 2007
have not released the total energy accumulated since 1746. From this scenario, the maximum tsunami
height could be 7.8 m in Huacho station with a minimum arrival time of 25 min after the earthquake.
In all the cases, we found that the tsunami travels faster to the south and slower to the north of Peru.
The tsunami simulation using the bathymetry data of 30 arc-second resolution showed longer travel
time and higher amplitude compared with the 1 arc-minute resolution, giving the former better resultsin the comparison between the synthetic and observed tide gauge records for the 1974 and 1966
events.
Keywords: Tsunami hazard in Peru, Tsunami simulation, Tsunami height, Tsunami arrival time.
1. INTRODUCTION
Recent catastrophic tsunamis in Sumatra 2004 (Mw9.0), Chile 2010 (Mw8.8) and Japan 2011(Mw9.0)
have shown the potential of the tsunami hazard, more destructive than the ground shaking by theearthquakes. These three earthquakes demonstrate the necessity of considering different scenarios andhistorical events, taking the most extreme cases into account in order to avoid an underestimation as
the last tsunami in Japan 2011. In this study, we estimate a more realistic tsunami hazard in the Central
coast of Peru using numerical simulations of two instrumentally recorded events in 1974, 1966 andhistorical one in 1746. Moreover, we adopt a realistic tsunami scenario using the interseismic plate
coupling facing Huacho, Lima and Pisco cities. The estimated moment deficit could produce anearthquake of Mw 8.7 in the future.
Geophysical Institute of Peru, Lima – Peru.
International Institute of Seismology and Earthquake Engineering, Building Research Institute, Japan.

2. DATA
In order to perform numerical tsunami simulation, we use three kinds of data. The first one is thebathymetry data from the General Bathymetry Chart of the Ocean (GEBCO), which is useful to knowthe morphology of the sea bottom, taking into account that the velocity of the tsunami depends on sea
bottom depth. Also, in order to compare the accuracy of bathymetry, we use GEBCO 1 arc-minute and30 arc-second resolution data. The second one is the tide gauge record which is important in order tovalidate our result in tsunami simulation and get a better approximation of the tsunami source. For the1966 event we use the tide gauge records of Chimbote (09°14’S; 79°00’W), Callao (12°03’S;77°09’W) and San Juan (15°21’; 75°10’). For the 1974 event we use Callao and San Juan records. Alltide gauges are operated by the Directorate of Hydrography and Navigation (DHN), the Navy of Peru,
which is responsible for the National Tsunami Warning System. Moreover, in order to estimate theheight and arrival time of the tsunami along the central coast of Peru, we consider the location of theactual tide station and we assume some stations in important places along the study area. In order tocompare the synthetic tsunami waveforms with the observed ones we digitize the tide gauge records
provided by Kuroiwa (2004) and Murty and Wigen (1975) and removed the tide effect fitting apolynomial function and subtracting the tide from the original signal for the 1974 and 1966 events.
3. METHODOLOGY
3.1. Computational Area
For the instrumental 1966 and 1974 events, the computational domain ranges from 84.0°W to 74.0° W
and from 17°S to 7°S (600 x 600 for 1 arc-minute and 1200 x 1200 for 30 arc-second grid nodes). For
the historical 1746 event, the computational domain ranges from 91°W to 72°W and from 20°S to 4°S(1140 x 960 for 1 arc-minute and 2280 x 1920 for 30 arc-second grid nodes). Time step of 2s for 1
arc-minute and 3s for 30 arc-second were chosen considering the CFL (Courant-Friedrichs-Lewy)
criteria, in order to avoid numerical instabilities. The propagation time of 3 hours has been chosen inorder to simulate enough duration of waves for comparison with the tide gauge records for all the threecases.
3.2 Tsunami Source
In order to calculate the static deformation of the seafloor, which is used as an initial condition, we use
the algorithm by Okada (1985) based on the assumption of an isotropic media with a half-space.
Using nine source parameters we can calculate the seafloor deformation due to the fault motion. These
parameters are latitude, longitude, depth of fault top, length, width, strike, dip, rake angle and slip
amount. In order to get the best parameters for our simulation, we consider the geometry of the Nazca
plate subduction in the central region between 10°S and 15°S on which the seismicity distribution
shows a dip of 10° at a depth of 20-25 km and increases to 30° until a depth of about 100 km, where it
became sub-horizontal (Barazangi and Izacks, 1976).
4. RESULTS AND DISCUSSION
4.1. Tsunamis on 3 October 1974 and 17 October 1966
4.1.1 Tsunami Source
In order to find a good source model for the 1974 and 1966 events we perform a tsunami simulationand stimate the tsunami height and arrival time. In both cases we use the scaling law proposed by
Papazachos et al. (2004) in order to know the size of the fault considring the estimated moment
magnitude for this events. Since it is a rough estimation of the source model, we refer previous studiessuch as aftershock distribution, rupture distribution (Hartzell and Langer, 1994; Langer and Spence,

1995) to improve the source models as the resoult of comparison between synthetic tsunami
waveforms and recorded ones.
b)a)

B

1966

Cross section A-BA1974

BA

Figure 1: a) Seismic fault models proposed for 1974
and 1966 events and projection to the surface(yellow rectangle), the epicentral location by USGS
(yellow star), the uplift and subsidence areas withthe contour interval of 0.1 m and aftershocks andrupture areas (dark green and light green dashedlines). b) Cross section of the vertical deformation
along A - B.

After numerous simulations we find a good
agreement between the synthetic andrecorded waveforms, and propose source
models for the event in 1974 and 1966
located to the south and north of Lima city,respectively (Table 1). According to theseparameters
thecalculated
seafloor
deformation showed an uplift of 0.92 m and a
subsidence of 0.52 m for the 1974 event, and2.33 m and 0.42 m for the 1966 event. In
both cases we compare the proposed source
models with the aftershock distribution areas
determined by Langer and Spence (1995).
The aftershock and rupture area in both cases
are located within our proposed sourcesindicating good agreement with our result(Figure 1a and b). Moreover, the proposedmodel for the 1966 event with a small lengthand large width is in good agreement with themodel proposed by Abe (1972) using long
period surface wave data recorded in far fieldstations.

4.1.2 Tsunami arrival time and maximum height
Tsunami Arrival Time (min)Maximum Tsunami Height (m)1 arc-minute

TAT MTH

30 arc-second

Figure 2: Distribution of the maximum tsunami height (left) andcomparison of the tsunami arrival time for the first wave andmaximum tsunami height (right) using the bathymetry data of 30
arc-second (red) and 1 arc-minute (blue), for the 1974 event.

The tsunami arrival times
calculated by using thebathymetry data of 30
arc-second tend to be larger
than the ones obtained byusing the bathymetry data of
1 arc-minute. Figure 2 forthe 1974 event the maximum
tsunamiheightswereestimated at the stations ofCallao (0.8 m), Pucusana(1.14 m) and Cerro Azul(1.46), since the maximumdirectivity of the tsunami
energy is perpendicular tothe strike angle (Figure 2).
Theminimum
tsunamiarrival time is 30 min after
the earthquake in the Cerro
Azul station.

For the 1966 event, between
Salaverry (8.5°S) and Callao(11.5°S), the maximum
tsunami height of 1.1 - 1.9 m
wascalculated,withtheexceptionof
themaximum tsunami height of
0.8 m at Ancon station(Figure3).
Thischaracteristic shows a good
agreement with the survey
between Ancon and Huacho
where low amplitude oftsunami
wasobserved
Maximum Tsunami Height (m)(Lomnitz and Cabre, 1968).
TAT MTHThe high amplitude of
1 arc-minute30 arc-second
tsunami in Callao station(1.9 m) gives us an importantfactor of amplification in
Figure 3: Same as Figure 2 but for the 1966 event.
front of Callao city. Finally,small waves (<0.8 m) arecalculated to the south.
In both cases, the maximum tsunami height calculated by using the bathymetry data of 30 arc-second
tends to be higher than the one obtained by using the bathymetry data of 1 arc-minute.
Tsunami Arrival Time (min)Table 1: Proposed fault parameters for the 1974 and 1966 earthquake using tsunami simulation.
Year1974
1966

Lat.
(° S)
13.9
11.0Long.
(° W)
77.4
79.0

Slip(m)2.4
4.9

Length(km)185
70Width(km)75
130

Strike(°)
325
330

Dip(°)
1020Rake(°)
9090

Top depth(km)974.2 Historical Tsunami on 28 October 1746
A study of historical events after the 2011 tsunami in Japan is more important considering that thelarge events have some degree of cyclicality in terms of frequency and magnitude. We perform atsunami numerical simulation for the historical 1746 event as a possible event in the future. We carriedout a rough validation of the tsunami model using the historical descriptions of the damages. Moreover,the estimated moment magnitude for this event according to previous studies is between 8.5 to 9.5. Inorder to find more precise magnitude and fault model we performed the tsunami simulation for four
scenarios, considering the moment magnitude of 8.5, 8.8, 9.0 and 9.2 (Table 2). Dorbath et al. (1990)
indicate that this event ruptured along 350 km and produced a tsunami with local height of 15 m to 20m, destroying Lima completely.

Mw
8.8
9.0

Table 2: Fault parameters of the four scenarios for the 1746 earthquake
Lat.
Lon.
Slip
LengthWidth Strike
DipRake
Top depth
(° S)
(° W)
(m)
(km)
(km)
(°)
(°)
(°)
(km)
-78.0-13.3
14330
100
328
10900
-78.0
-13.3
25350
10032810900

However, according to a historical tsunami description it could have a height of around 7 m. The more
preferable scenarios could be the case of Mw=8.8 with the calculated tsunami height of 6.5 m at

Callao or the cases of Mw=9.0 with the one of 9.8 m at Callao. For these two scenarios, the maximum
tsunami height more than 3 m can be shown between Huarmey to Cerro Azul stations.
4.3 Scenario from GPS interseismic coupling
4.3.1 Slip distribution and vertical seafloor deformation
A slip distribution model was provided by Pulido et al. (2011) from the interseismic coupling modelusing GPS data. Figure 4a shows the slip distribution with two nearest asperities. The first one is to thenorth between 11°S-12.5°S and the second one is to the south between 12.5°-15°S. According to thedeficit of the estimated seismic moment (12 x 1021 Nm), both asperities could produce an earthquakeof Mw=8.7. In order to identify the contribution of each asperity to tsunami height and arrival time, weperformthetsunami
simulations for both twoa)b)asperities and only theasperity to the north.
Figure 4b shows the total
1966
vertical deformation for
the two asperities, which
produce an uplift of 4.6 m
and a subsidence of 2.2 m.
2007
The distribution of the1974
tworuptureareas
proposed in this study forthe events in 1974 and1966 are located aroundthe asperity to the north(in a low coupling area)
Figure 4: a) Slip distribution from GPS data provided by Pulido et al. and the earthquake in(2011), the rectangles and polygon show the source model for the 1966 2007 is located over theand 1974 events proposed in this study and the 2007 proposed by Sladen south asperity in front of
et al. (2010). b) Uplift and subsidence areas with contour interval of 0.3 Pisco city.
m for the two asperities located offshore form Huacho to Pisco
4.3.2 Tsunami arrival time and maximum height
Tsunami Arrival Time (min)Maximum Tsunami Height (m)TAT MTH

30 arc-second

Figure 5: Same as figure 2 but for the two asperity model from GPSdata.

Figure 5 shows themaximum
tsunamiamplitude and arrival time
considering
thetwoasperities. According tothis scenario, the stations
facing the source area will
be greatly affected. In
bothscenarios
thecomputation results aresimilar in the north of therupture area from Eten to
Barranco stations with theminimum arrival time of20
minaftertheearthquake
andthemaximum tsunami heightof about 7.8 m in Huachostation.

For the places to the north and south of the two asperities, the tsunami will be relatively small, lessthan 2 m. For the scenario without considering the asperity in the south, the maximum tsunami wave
decreases to 2.5 m and 1 m in Cerro Azul and Pisco stations, respectively. The scenario considering
the two asperities, the tsunami arrival time in the Pisco station is almost at the same time with theearthquake occurrence, this characteristic is due to location of the south asperity under the Piscostation. The scenario considering only the asperity to the north, the first tsunami wave will reach thecoast along the Huarmey station within 18 min and from Huarmey to Barranco between 20 and 30 min
after the earthquake. The places to the south, from the Cerro Azul to Atico stations the first tsunami
waves arrive in 35 min and later. The places to the north of Lima between Chimbote and Eten haveenough time more than 1 hour to evacuate. The tsunami propagation shows the same behavior with theprevious cases, which the tsunami propagation to the north takes more time with respect to the southof Peru. The tsunami arrival time is more than one hour for the stations located to the north (Chimboteand Salaverry), but it is less than one hour for the stations located to the south (Puerto Caballa and SanJuan).
5. CONCLUSIONS
We assessed the tsunami hazard in the central coast of Peru using two recent (1974, Mw8.0; 1966,Mw8.1) and one historical tsunami (1746, Mw 8.5-9.2). The historical 1746 events, according to thetsunami simulation and historical description of the tsunami damages in Callao city, could have been
the earthquake of Mw 8.8-9.0. Moreover, we adopted more realistic tsunami scenarios, based on theslip distribution from the interseismic coupling predicted from GPS data (Pulido et al., 2011). In orderto analyze the accuracy of the tsunami amplitude and arrival time, we used two bathymetry data fromGEBCO with 1 arc-minute and 30 arc-second grid intervals. We simulated the tsunamis in 1974 and1966 and we proposed the best solutions of the tsunami sources based on the comparison of thesynthetic and recorded tsunami waveforms. According to their locations, both events are emplacednear Lima city and around the predicted coupling area. This characteristic seems that these two events
released the accumulated energy to the north and south of the coupling area. In this sense, weperformed the tsunami simulation using the slip distribution model in order to evaluate two realistic
scenarios of the future tsunami which could be used to construct a tsunami hazard map and evacuation
plan in the Callao city. According to these scenarios, the most affected areas are located between
Puerto Supe and Barranco with maximum tsunami height of 7.8 m in Huacho station. The minimum
time to evacuate for those places near the source is about 15 min in average.
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