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2022. 18(2). 161-171 Строительная механика инженерных конструкций и сооружений Structural Mechanics of Engineering Constructions and Buildings
ISSN 1815-5235 (Print), 2587-8700 (Online)
http://journals.rudn.ru/structural-mechanics
Сейсмостойкость сооружений Seismic resistance
DOI 10.22363/1815-5235-2022-18-2-161-171 UDC 699.841
RESEARCH ARTICLE / НАУЧНАЯ СТАТЬЯ
Macroseismic intensity-based catalogue of earthquakes in Ecuador
David Cajamarca-Zuniga1'2 Oleg Kabantsev2 , Christopher Marin1
lCatholic University of Cuenca, Cuenca, Republic of Ecuador
2National Research Moscow State University of Civil Engineering, Moscow, Russian Federation [email protected]
Article history
Received: November 21, 2021 Revised: February 12, 2022 Accepted: February 29, 2022
For citation
Cajamarca-Zuniga D., Kabantsev O., Marin C. Macroseismic intensity-based catalogue of earthquakes in Ecuador. Structural Mechanics of Engineering Constructions and Buildings. 2022;18(2):161-171. http://doi.org/10.22363/1815-5235-2022-18-2-161-171
Abstract. Earthquake magnitude catalogues and peak ground acceleration (PGA) maps for Ecuador may be found in several studies, however, there are rare works on the characterisation of the epicentral macroseismic intensities associated with earthquakes. In view of the concept that macroseismic intensity enables us to categorise the extent and severity of damage to buildings and structures caused by an earthquake, this study aims to compile a macro-seismic intensity-based catalogue of earthquakes in Ecuador, characterise the epicentral macroseismic intensities associated to seismogenic sources and perform a comparison with the National Seismic Hazard Map. This paper is the first that presents a catalogue of earthquakes with macroseismic intensities >VII and a series of maps of earthquake epicentres according to intensity, focal depth, data and magnitude of seismic events in Ecuador, based on the study of historical and instrumental records from 1900 to 2021. The obtained data shows that 95% of the territory of Ecuador has a PGA > 0.1 g, which corresponds to seismic intensities greater than VII, while regions with seismicity >VIII (ag = 0.2 g) constitute 86%, and 3.8% of the territory of Ecuador has very high seismicity (>IX), where the PGA exceeds 0.5 g. This information suggests that the normative National Seismic Hazard Map of Ecuador underestimate the hazard mainly in the south-east and in the Central Andes of Ecuador, and require an actualization.
Keywords: earthquake, Ecuador, macroseismic intensity, seismic hazard, seis-micity, structural design
David Cajamarca-Zuniga, Docent of the Department of Civil Engineering, Catholic University of Cuenca, Ave Las Americas & Humboldt, Cuenca, 010101, Republic of Ecuador; PhD researcher, National Research Moscow State University of Civil Engineering, 26 Yaroslavskoye Shosse, Moscow, 129337, Russian Federation; ORCID: 0000-0001-8796-4635, Scopus ID: 57251506300, WoS ID: AA0-8887-2020, eLIBRARY SPIN-code: 6178-4383; [email protected]
Oleg V. Kabantsev, Doctor of Technical Sciences, Professor, National Research Moscow State University of Civil Engineering, 26 Yaroslavskoye Shosse, Moscow, 129337, Russian Federation; ORCID: 0000-0001-9907-8470, Scopus ID: 15055871000, WoS ID: T-3937-2017, eLIBRARY SPIN-code: 21141185; [email protected]
Christopher Marin, civil engineer, master student of the Department of Civil Engineering, Catholic University of Cuenca, Ave Las Americas & Humboldt, Cuenca, 010101, Republic of Ecuador; ORCID: 0000-0002-6601-032X; [email protected]
© Cajamarca-Zuniga D., Kabantsev O., Marin C., 2022
I This work is licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.Org/licenses/by-nc/4.0/legalcode
Каталог землетрясений Эквадора,
основанный на макросейсмической интенсивности
Д. Кахамарка-Сунига1'2 121,0.В. Кабанцев2 , К. Марин1
1Католический университет города Куэнки, Куэнка, Республика Эквадор
2Национальный исследовательский Московский государственный строительный университет, Москва, Российская Федерация > [email protected]
Аннотация. Каталоги магнитуд землетрясений и карты пиковых ускорений грунта (ПУГ, англ. PGA) для Республики Эквадор можно найти во многих исследованиях, однако работы, посвященные характеристике эпицентраль-ной макросейсмической интенсивности, связанной с землетрясениями, встречаются редко. В связи с тем, что макросейсмическая интенсивность позволяет классифицировать степень и тяжесть ущерба, нанесенного землетрясением зданиям и сооружениям, целями данного исследования стали: 1) составление каталога землетрясений в Эквадоре на основе макросейсмической интенсивности; 2) характеристика эпицентральных макросейсмических интенсив-ностей, связанных с сейсмогенными источниками; 3) сравнение с Национальной картой сейсмической опасности. Впервые представлены каталог землетрясений с макросейсмической интенсивностью >VII и серия карт эпицентров землетрясений в соответствии с интенсивностью, глубиной очага, данными и магнитудой сейсмических событий в Эквадоре, основанных на изучении исторических и инструментальных записей с 1900 по 2021 г. Полученные данные показывают, что 95 % территории Эквадора имеют PGA > 0,1 g, что соответствует сейсмической интенсивности более VII, регионы с сейсмичностью >VIII (ag = 0,2 g) составляют 86 %, а 3,8 % территории Эквадора имеют очень высокую сейсмичность (>IX), где PGA превышает 0,5 g. Это свидетельствует о том, что нормативная Национальная карта сейсмической опасности Эквадора не учитывает опасность в основном на юго-востоке и в Центральных Андах Эквадора и требует актуализации.
Ключевые слова: землетрясение, Эквадор, макросейсмическая интенсивность, сейсмическая опасность, сейсмичность, сейсмостойкое проектирование
Introduction
The greatest earthquakes are known to occur at the tectonic plate interface of subduction zones. Ecuador is located at the northwest interface of the South American tectonic plate whit the Nazca tectonic plate. This zone is part of the Rim of Fire, which is the world's most seismically active region. In this region about 90% of all earthquakes and about 80% of the strongest earthquakes have occurred1 [1]. The Andes are one of the highest seismic activity regions in the world, accounting for around 20% of the Earth's total released seismic energy [2]. About 90% of continental territory of Ecuador presents high seismic hazard. The subduction of the Nazca tectonic plate and the complex system of active geological faults generates mostly shallow earthquakes in Ecuador, where the 7th world's largest earthquake was registered in 1906 (Mw = 8.8) [3; 4].
The definition of seismic hazard is fundamental to study the influence of the seismicity of a given region on earthquake-resistant structural design. In this work we present a catalogue of macroseismic events with intensities
Кахамарка-Сунига Давид, доцент департамента строительства, Католический университет города Куэнки, Республика Эквадор, 010101, Куэнка, Ave Las Americas & Humboldt; аспирант, Национальный исследовательский Московский государственный строительный университет, Российская Федерация, 129337, Москва, Ярославское шоссе, д. 26; ORCID: 0000-0001-8796-4635, Scopus ID: 57251506300, WoS ID: AA0-8887-2020, eLIBRARY SPIN-код: 6178-4383; [email protected]
Кабанцев Олег Васильевич, доктор технических наук, профессор, Национальный исследовательский Московский государственный строительный университет, Российская Федерация, 129337, Москва, Ярославское шоссе, д. 26; ORCID: 0000-0001-9907-8470, Scopus ID: 15055871000, WoS ID: T-3937-2017, eLIBRARY SPIN-код: 2114-1185; [email protected]
Марин Кристофер, инженер-строитель, магистр, Инженерный факультет, Католический университет города Куэнки, Республика Эквадор, 010101, Куэнка, Ave Las Americas & Humboldt; ORCID: 0000-0002-6601-032X; [email protected]
1 United States Geological Survey. 20 Largest Earthquakes in the World. USGS. Earthquake Hazards. Available from: https://www.usgs.gov/natural-hazards/earthquake-hazards/science/20-largest-earthquakes-world?qt-science_center_objects=0#qt-science_center_objects (accessed: 20.02.2020).
История статьи
Поступила в редакцию: 21 ноября 2021 г. Доработана: 12 февраля 2022 г. Принята к публикации: 29 февраля 2022 г.
Для цитирования
Cajamarca-Zuniga D., Kabantsev O., Marin C. Macroseismic intensity-based catalogue of earthquakes in Ecuador // Строительная механика инженерных конструкций и сооружений. 2022. Т. 18. № 2. С. 161-171. http://doi.org/10.22363/1815-5235-2022-18-2-161-171
greater than VII based on the study of seismogenic sources of Ecuador and its relation with the epicentres of historical high intensity earthquakes in order to compile a catalogue and maps of epicentres of earthquakes by intensities, years, depth and magnitudes, and compare the seismic events with the normative National Seismic Hazard Map of Ecuador.
To compile this catalogue, we reviewed pre-instrumental and instrumental information from several local, regional, and global sources such as IG-EPN, CERESIS, EHB, ISS, ISC, CENTENNIAL, NEIC, GCMT, USGS, and from other scientific works.
Based on the compiled catalogue, we have developed some maps of earthquakes locations according to registered intensities. In this paper, we also present the maps of epicentres of earthquakes by their intensities, years, depth and magnitudes, as well as comparison of the seismic events with both the normative National Seismic Hazard Map of Ecuador and the latest map of seismic hazard developed by the Ecuadorian Institute of Geophysics of the National Polytechnical School issued in 2021.2
Geodynamics of Ecuador and seismogenic sources
It is established that in the Equatorial latitudes the subducting process of the Nazca plate beneath the South American tectonic plate (55-75 mm/year) is the main and most evident geodynamic process in the northwestern region of South America and in the territory of Ecuador (Figure 1) [5-8].
Figure 1. Tectonic setting, major faults and relative plate motions in Ecuador. Locations of the 1906 earthquake (Mw = 8.8, black star); from north to south the 1979, 1958, 2016, 1942, 1901, 1953 earthquakes (M > 7.8, red circles)
Source: edited after Gutscher et al., 1999 [7].
The segment of the Northern Andes where both thrust faulting and crustal shortening are observed coincides with the subduction zone of Carnegie Ridge. Along the subandean zone and the eastern cordillera of Ecuador, a large system of thrusts, as well as strike-slip and transpressive faults is located [9; 10]. Three main seismogenic sources affect the seismicity of Ecuador. The subduction of the oceanic Nazca plate beneath the continental South American plate is the major geodynamic process which controls the tectonic setting of this region and originates two other seismogenic sources: the subduction and collision of the Carnegie Ridge (CR), and the segmentation and "escape" of the North Andean Block (NAB) with an intricate strike-slip fault system [11]. The Ecuadorian Andes mainly defines a compression zone featured by reverse faults in the foothills essentially orthogonal to the plate convergence vectors and
2 Catalogue of earthquakes in Ecuador. Mapa digital interactivo de peligro sísmico para Ecuador. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN); 2021. Available from: https://www.igepn.edu.ec/mapas/sismicidad/mapa-peligro-sismico (accessed: 23.09.2021).
slip faults as the Dolores-Guayaquil Megashear (DGM) [12; 13] and the Chingual-Cosanga-Pallatanga-Puna (CCPP) fault system [8; 14], which are segments of the Guayaquil-Caracas Continental Megashear (GCM).
The subduction of the Carnegie Ridge controls the locations of large earthquakes and the clusterisation of seismic activity along the northwest coastline of Ecuador, as well as the evolution of the foothill basins of Borbon and Manabi, the uplifting of both the coast region and the Pastaza-Napo region at the Amazon basin [15-17]. The schematic geological cross-section of the subduction process at the collision zone of Carnegie Ridge between latitudes 1°N-2°S suggested in [18] shows geological events related to this process (Figure 2).
Figure 2. West-East cross-section of Ecuador at 1°11' S, showing geological events related to Carnegie Ridge subduction [18]
In the collision zone of the Carnegie Ridge, the orientation of crustal faults changes from north-south to northeast-southwest along the subduction margin [15; 19]. The morphology of the Ecuadorian subandean zone and
its strong tectonic activity can be attributed to a major geody-namic event, such as the subduction of Carnegie Ridge. The bulldozing effect associated to the subduction of the CR has contributed to uplift of the coastal ranges at rates of 0.30-0.50 mm/year for the Peninsula of Manta [20], and generates the northeastward displacement of the NAB along the Guayaquil-Caracas Continental Megashear [21].
To understand the geodynamic scheme of Ecuador, it is necessary to consider the movement of North Andean Block as a detaching "mini-plate" sliding through the northwest corner of South America on a large right-lateral strike-slip fault. This tectonic block is bordered on the north by the South Caribbean deformed belt, on the west by the Colombia-Ecuador trench and Panama Block, and on the east by the Guayaquil-Caracas Continental Megashear. As a result of this process the NAB is being ejected to the northeast following the front of the Eastern Cordillera along a transpressive system of faults [22-25]. According to recent studies [8; 23; 24; 26], the NAB is migrating relatively fast, just as the Nazca Plate is subducting to the east relative to the Amazonian Craton, the NAB is migrating to the north-east in relation to the South American plate at 6-10 mm/year. The Guayaquil Gulf opens at the southern junction between two fracture zones (the Colombia-Ecuador Trench and the GCM) that isolate the NAB [22]. The east Andean front fault zone starts east of the Gulf of Guayaquil as the dextral Pallatanga Fault [27-29]. Northern this fault continues as the Chingual-La
Figure 3. Chingual - Cosanga - Pallatanga - Puna (CCPP) fault system [8]
Sofia Fault [5; 8; 27; 28]. The motion of the North Andean Block "produces a complex system of active faults that generate shallow-focus earthquakes on the eastern front of the Andes" [21; 26].
The Chingual-Cosanga-Pallatanga-Puna fault system (Figure 3) is the most developed fault system in the territory of Ecuador and defines the NAB eastern tectonic border in Ecuador, where several shallow earthquakes have been registered [27]. The CCPP fault system extends from Guayaquil Gulf in Ecuador to the eastern "Cordillera Real" on the border between Ecuador and Colombia [8], then continues into Colombia as the Algeci-ras Fault [24]. It should be noted that multiple large earthquakes have occurred in the north-south trending segments of the CCPP fault and in the Carnegie Ridge collision zone. The shear zone of CCPP accounts for high cortical seismic activity in the central-northern Andes Cordillera of Ecuador.
Results and discussion
The main seismogenic source in Ecuador is the subducting process of the Nazca tectonic plate beneath the South American continental plate. In the background of this process, is important to consider two factors: the influence of the Carnegie Ridge, which causes a "ploughing" effect (expression suggested by D. Cajamarca-Zuniga) on the shoreline and deep seismic activity in the Pastaza-Napo region at the Amazon basin, and the northward drift of North Andean block, which generates an intricate system of active strike-slip faults and generates shallow-focus earthquakes along the CCPP fault system.
The shoreline of Ecuador experienced large and great megathrust earthquakes along the northern flank of Carnegie Ridge collision zone: 1906 (Mw 8.8, intensity IX), 1942 (Mw 7.8, intensity IX), 1958 (Mw 7.7, intensity VIII), 1979 (Mw 8.2, intensity VIII), 2016 (Mw 7.8, intensity IX) [3; 30].
The central-north Andean region of Ecuador shows high crustal activity and registers multiple large historical earthquakes along the NNE-trending zone of CCPP fault system. Earthquakes with epicentral macroseismic intensity > VIII have occurred in 1541, 1557, 1575, 1587, 1645 (Mw 7, intensity IX), 1698 (Mw 7.7, intensity IX), 1755, 1757, 1797 (Mw 8.3, intensity XI), 1834, 1868 (Mw 7, intensity IX), 1923, 1926, 1938 (Mw 6.3, intensity VIII), 1949 (Mw 6.7, intensity X), 1996 (Mw 5.5, intensity VIII) [10; 31], mainly along NE-SW fault systems governed by the Guayaquil-Caracas Continental Megashear.
Figure 4. Location and years of earthquakes with macroseismic intensities >VII from 1900 to 2021. Here we can see the major
seismic intensity at the collision zone of the subducting Carnegie Ridge (CR), as well as along the CCPP fault system
Figure 5. Plane and cross-sectional locations of 130-300 km depth earthquakes, that show the inferred 400 km prolongation of Carnegie Ridge beneath the territory of Ecuador
The sub-Andean zone at the Amazon basin shows an intermediate-depth seismicity in the Pastaza-Napo region and a high shallow-focus activity to the south, between the Macas and Quito-Napo fault systems: 1961 (Mw 6.6,
intensity VIII), 1971 (Mw 7.4, intensity VII), 1987 (Mw 6.4, intensity IX), 1995 (Mw 6.5, intensity VIII), 2019 (Mw 7.5, intensity VII)3 [32; 33].
In the Figure 4 we present a map developed in ArcMap software and show the epicentres and years of earthquakes with macroseismic intensities > VII from 1900 to 2021, where we can see the major seismic intensity at the Carnegie Ridge collision zone, as well as along the CCPP fault system.
82* W 80" W 78° W 76* W
Figure 6. Locations and depth of earthquakes with intensities >VII from 1900 to 2021
78° W
76* W
82° W
78° W
Main crustal fault systems in Ecuador
- El Arigel-Huayrapungo-Nanegal-Apuela fault systems
.-Quito-Latacunga fault-fold system
— Macas fault system
-Cutucu-Napo fault system (Eastern Subandean Belt ESB}
— Chingual-Cosanga-Paltatanga-Puna fault system (NAB limit)
S™0" r*™
IS3 '
J «°"200á
' 2011 19^7 02012
C(l 9^31953 6Q99 OQ2017 ' ' 020^8119& ^ 01982 02006
~995 O ITS C^pi 2Q19-
199№0 C1963 O
0 50 100
82° W
80° W
Main crustal fault systems in Ecuador
-El Angel-Huayrapungo-Nanegal-Apuela fault systems . ^—Quito-Latacunga fault-fold system — Macas fault system
-Cutucu-Napo fault system (Eastern Subandean Belt ESB)
—Chingual-Cosanga-Pallatanga-Puna fault system (MAB limit)
fflW*5.7)nVII (V-5) Vll (6*^1 (5.7) V VI (5.6} o
VI (5.5) Cv (S.5) V| ,5.5 0 50 100 200 km
82" W
80" W
b
Figure 7. Location and years of earthquakes with intensities >III from 1900 to 2021 (a) and location, depth, intensity and magnitude of earthquakes with intensities >III from 1900 to 2021 (b)
3 United States Geological Survey. Earthquake catalog. USGS. Earthquake Hazards program. Available from: https://earthquake.usgs.gov/earthquakes/search/ (accessed: 30.07.2021); Catálogo Homogenizado 1587-2011. Sismicidad. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN). Available from: https://igepn.edu.ec/mapas/sismicidad/mapa-catalogo-homogenizado (accessed: 30.07.2021).
a
Catalogue of 1900-2021 Ecuador earthquakes with macroseismic intensities >VII
Date, Time, Intensity, Magnitude Scale Depth, Location Latitude, Longitude,
dd/mm/yyyy UTC MMI km ° °
1587 VIII 6.3 Mw 20 km NNE of Quito. Ecuador 0.00 -78.40
1645 IX 7 Mw 11 km E of Riobamba. Ecuador -1.68 -78.55
1674 VIII 6.3 Mw 17 km WbS of Riobamba. Ecuador -1.70 -78.80
1687 VIII 6.3 Mw 39 km ENE of Ambato. Ecuador -1.10 -78.30
1698 IX 7.7 Mw 15 km ESE of Banos. Ecuador -1.45 -78.30
1736 VIII 6.3 Mw 25 km WNW of Latacunga. Ecuador -0.80 -78.80
1749 VIII 6.3 Mw Loja, Loja. Ecuador -4.00 -79.20
1755 VIII 6.3 Mw Quito, Pichincha. Ecuador -0.21 -78.48
1757 VIII 7 Mw 7 km S of Latacunga. Ecuador -1.00 -78.60
1786 VIII 6.3 Mw 6 km WNW of Riobamba. Ecuador -1.65 -78.70
1797 XI 8.3 Mw 15 km WbS of Baños. Ecuador -1.43 -78.55
1859 VIII 6.3 Mw 26 km W of Otavalo. Ecuador 0.20 -78.50
1868 IX 7 Mw 10 km SW of Ibarra. Ecuador 0.30 -78.20
1868 VIII 6.3 Mw 7 km WSW of El Angel. Ecuador 0.60 -78.00
1896 IX 7 Mw 4 km S of Canoa. Ecuador -0.50 -80.45
31/01/1906 15:36:10 IX 8.8 Mw 20 22 km NW of Atacames. Ecuador 1.00 -80.00
1911 VIII 1 Mw 6 km WSW of Riobamba. Ecuador -1.70 -78.70
1913 VIII 6.3 Mw 31 km NW of Loja. Ecuador -3.80 -79.40
1914 VIII 7 Mw 30 km S of Quito. Ecuador -0.50 -78.50
1923 VIII 6.3 Mw 30 km S of Quito. Ecuador -0.50 -78.50
1926 VIII 6.5 Mw 20 km W of Tulcan. Ecuador 0.80 -77.90
1929 VIII 6.3 Mw 19 km SSW of Quito. Ecuador -0.40 -78.55
02/10/1933 15:29:27 VII 6.7 Mw 15 43 km N of Santa Elena. Ecuador -1.83 -80.85
1938 VIII 6.3 Mw 15 km SE of Quito. Ecuador -0.30 -78.40
14/05/1942 02:13:27 IX 7.8 Mw 20 10 km SW of Pedernales. Ecuador 0.01 -80.12
23/10/1944 23:40:09 VII 6.7 Mw 20 35 km NNE of Quininde. Ecuador 0.61 -79.32
05/08/1949 19:08:52 X 6.7 Mw 15 20 km NE of Baños. Ecuador -1.25 -78.32
12/12/1953 17:31:29 VIII 7.3 Mw 25 14 km NNE of Zorritos. Peru -3.55 -80.64
11/05/1955 11:04:04 VII 6.5 Mw 15 42 km SE of Cayambe. Ecuador -0.23 -77.88
20/07/1955 21:00:47 VII 6 Mw 15 14 km W of Cotacachi. Ecuador 0.30 -78.39
16/01/1956 23:37:45 VII 7 Mw 20 7 km NNE of Tosagua. Ecuador -0.73 -80.21
19/01/1958 14:07:28 VIII 7.6 Mw 27.5 19 km ENE of Esmeraldas. Ecuador 1.01 -79.49
19/01/1958 14:43:30 VII 6.8 Mw 27.5 23 km NE of Esmeraldas. Ecuador 1.15 -79.54
14/04/1958 21:32:34 VII 6.8 Mw 25 30 km SE of Esmeraldas. Ecuador 0.80 -79.43
28/07/1961 01:05:31 VIII 6.6 Mw 142.1 47 km E of Taisha. Ecuador -2.29 -77.04
19/05/1964 23:03:40 VIII 6.2 Mw 35 7 km WSW of Calceta. Ecuador -0.86 -80.23
09/02/1967 15:24:49 IX 7 Mw 55 162 km NNE of Florencia. Colombia 2.85 -74.80
19/06/1968 08:13:35 VII 6.8 Mw 15 49 km NNW of Moyobamba. Peru -5.61 -77.09
10/12/1970 04:34:41 IX 7.2 Mw 25 15 km SE of Cainaveral. Peru -4.03 -80.54
27/07/1971 02:02:49 VII 7.4 Mw 120 103 km ESE of Sucua. Ecuador -2.84 -77.32
02/10/1974 02:54:59 VII 5.7 Mb 5 48 km SW of Sechura. Peru -5.91 -81.09
09/04/1976 07:08:47 VIII 6.7 Ms 9 25 km SW of Esmeraldas. Ecuador 0.78 -79.80
06/10/1976 09:12:38 VIII 5.7 Mb 33 16 km NW of Saquisili. Ecuador -0.75 -78.78
24/03/1978 12:31:22 VII 5.3 Mb 42 9 km E of Lagunas. Peru -5.22 -75.59
12/12/1979 07:59:03 VIII 7.7 Ms 24 68 km WNW of San Lorenzo. Ecuador 1.60 -79.36
31/03/1983 13:12:52 VIII 5.5 Mb 22.2 8 km WNW of Popayan. Colombia 2.46 -76.69
12/04/1983 12:07:54 VII 7 Mw 104.2 92 km NNE of La Peca. Peru -4.84 -78.10
22/11/1983 14:21:03 VII 6.6 Mw 54.9 21 km SE of Muisne. Ecuador 0.48 -79.88
25/12/1983 05:32:40 VII 5.4 Mb 33 49 km SSE of Saquena. Peru -5.09 -73.36
06/03/1987 08:14:48 VII 6 Mw 8.5 24 km E of Cayambe. Ecuador 0.02 -77.93
06/03/1987 01:54:50 VII 6.4 Mw 14.1 49 km SE of Pimampiro. Ecuador 0.05 -77.65
06/03/1987 04:10:41 VII 7.2 Mw 10 29 km SSE of Pimampiro. Ecuador 0.15 -77.82
22/09/1987 13:43:37 IX 6.4 Mw 10 26 km W of Tena. Ecuador -0.98 -78.05
22/09/1987 16:21:35 VII 6 Mw 10 36 km WSW of Tena. Ecuador -1.08 -78.13
30/05/1990 02:34:05 VII 6.6 Mw 24.2 28 km E of Moyobamba. Peru -6.02 -77.23
02/09/1990 04:26:48 VII 6.6 Mw 14.2 34 km SW of Pedernales. Ecuador -0.14 -80.28
04/04/1991 15:23:20 VII 6.5 Mw 20.7 4 km ENE of Rioja. Peru -6.04 -77.13
05/04/1991 04:19:49 VII 7.1 Mw 19.8 11 km NE of Rioja. Peru -5.98 -77.09
06/06/1994 20:47:40 IX 6.8 Mw 12.1 23 km E of Toribio. Colombia 2.92 -76.06
03/10/1995 12:44:58 VIII 6.5 Mw 16.7 50 km SE of Sucua. Ecuador -2.78 -77.85
03/10/1995 01:51:23 VII 7 Mw 24.4 45 km SE of Sucua. Ecuador -2.75 -77.88
07/10/1995 21:28:03 VII 5.8 Mw 12.3 52 km SE of Sucua. Ecuador -2.78 -77.82
25/08/1996 14:09:03 VIII 5.5 Mwc 50.7 10 km WSW of Salcedo. Ecuador -1.08 -78.67
28/10/1997 06:15:17 VII 7.2 Mwc 112 51 km N of Barranca. Peru -4.37 -76.68
04/08/1998 18:59:20 VIII 7.2 Mwc 33 3 km E of Bahia de Caraquez. Ecuador -0.59 -80.39
21/01/2005 13:45:14 VII 6 Mwb 10 21 km WSW of Montecristi. Ecuador -1.13 -80.83
24/01/2005 23:23:26 VII 6.1 Mwb 16.9 23 km W of Jipijapa. Ecuador -1.36 -80.79
26/09/2005 01:55:37 VII 7.5 Mwb 115 39 km NW of Yurimaguas. Peru -5.68 -76.40
16/04/2016 23:58:36 IX 7.8 Mww 20.59 27 km SSE of Muisne. Ecuador 0.38 -79.92
20/04/2016 08:35:10 VII 6 Mwb 10 10 km N of Muisne. Ecuador 0.71 -80.04
22/04/2016 03:03:41 VII 6 Mww 10 34 km NNW of Bahia de Caraquez. Ecuador -0.29 -80.50
18/05/2016 07:57:02 VII 6.7 Mww 16 32 km SE of Muisne. Ecuador 0.43 -79.79
18/05/2016 16:46:43 VII 6.9 Mww 29.95 24 km NW of Quininde. Ecuador 0.49 -79.62
11/07/2016 02:11:04 VII 6.3 Mww 21 33 km NNW of Quininde. Ecuador 0.58 -79.64
19/12/2016 07:11:39 VII 5.4 Mwr 10 11 km SSW of Esmeraldas. Ecuador 0.88 -79.71
18/04/2017 17:49:55 VII 5.9 Mww 14 151 km NE of Alianza Cristiana. Peru -2.71 -75.30
30/06/2017 22:29:45 VII 6 Mww 13 35 km NNW of Bahia de Caraquez. Ecuador -0.28 -80.49
03/12/2017 11:19:05 VII 6.1 Mww 17 18 km NE of Bahia de Caraquez. Ecuador -0.47 -80.31
22/02/2019 10:17:23 VII 7.5 Mww 145 115 km ESE of Palora. Ecuador -2.19 -77.05
26/05/2019 07:41:15 VIII 8 Mww 122.57 78 km NE of Navarro. Peru -5.81 -75.27
30/07/2021 17:10:19 VII 6.2 Mww 32.66 9 km ESE of Sullana. Peru -4.93 -80.60
The geodynamic and seismic activity in the territory of Ecuador suggest that the prolongation of the CR and the geological expression of its subduction beneath Ecuador requires about 400 km from the Colombia -Ecuador - Peru trench. In the Figure 5 we show the locations of depth earthquakes epicentres according to data from the IG-EPN earthquake catalogue.4 Also, we suppose that the eastern interface boundary of the Carnegie Ridge under the territory of Ecuador may be a triple junction of the Nazca tectonic plate with the Farallon plate and the Amazonian Craton, which probably controls the intermediate-depth seismicity in the Pastaza-Napo region at the Amazon basin.
Regarding the influence of earthquakes on buildings and structures, the only magnitude of an earthquake does not allow us to understand the level of damage to the structures, as it depends on other factors. For understanding the effects of an earthquake on buildings and structures, it is important to know and understand the macroseismic intensity of earthquakes. This concept enables us to categorise the extent and severity of earthquake-related damage to structures. Below we present information and maps related to earthquakes in Ecuador from 1900 to 2021 according to the intensity, focal depth and magnitude of each event. The proposed maps were developed in ArcMap software for geospatial data processing.
In the Figure 6 we show the epicentres and depth of earthquakes with intensities >VII from 1900 to 2021. The Figure 7, a presents a map of earthquake epicentres with intensities >III and the corresponding year of each event from the 1900 to 2021. In the Figure 7, b we present a map that shows the depth, intensities and magnitudes of earthquakes with intensities >III from 1900 to 2021.
In the Table we present a catalogue of earthquakes with macroseismic intensities >VII based on historical and instrumental records from 1900 to date5 [2; 5; 14; 31; 32].
We provide a comparison intensity-based map of earthquakes with both, the National Seismic Hazard Map of the Ecuadorian Building Standard NEC-SE-DS 2015 (Figure 8) and the latest (non-normative) probabilistic seismic hazard map issued by the Institute of Geophysics of the National Polytechnic School of Ecuador in 20216 (Figure 9).
84° W 82° W 80° W 78° W 76° W
2" N ■ Intensity
(EMS-98) a 3
G A ® 5
O 6 O 7
O 8
• 9
G 10
• 11
2" s. Crustal Fault
-CCPP fault system
Seismic hazard (NEC-SE-DS 2015)
PGA; [% g] Tr=475-yr
■ 0.15 4.s. 0.25
0.3 0.35 ■I 0.4
■ 0.5
84° W 82° W 80" W 78° W 76" W
Figure 8. Comparison of earthquake epicentres by intensities >III with the Normative seismic hazard map of Ecuador (NEC-SE-DS 2015)
84* W 82* W 80* W 78* W 76* W
84° W 82" W 80° W 78° W 76° W
Figure 9. Comparison of earthquake epicentres by intensities >111
with the non-normative seismic hazard map issued by the Institute of Geophysics of the National Polytechnic School of Ecuador (IG-EPN, 2021)
4 Catalogue of earthquakes in Ecuador. Mapa digital interactivo de peligro sísmico para Ecuador. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN); 2021. Available from: https://www.igepn.edu.ec/mapas/sismicidad/mapa-peligro-sismico (23.09.2021).
5 United States Geological Survey. 20 Largest Earthquakes in the World. USGS. Earthquake Hazards. Available from: https://www.usgs.gov/natural-hazards/earthquake-hazards/science/20-largest-earthquakes-world?qt-science_center_objects=0#qt-science_center_objects (accessed: 20.02.2020); Catálogo Homogenizado 1587-2011. Sismicidad. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN). Available from: https://igepn.edu.ec/mapas/sismicidad/mapa-catalogo-homogenizado (accessed: 30.07.2021); Catalogue of earthquakes in Ecuador. Mapa digital interactivo de peligro sísmico para Ecuador. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN); 2021. Available from: https://www.igepn.edu.ec/mapas/sismicidad/mapa-peligro-sismico (23.09.2021).
6 Catalogue of earthquakes in Ecuador. Mapa digital interactivo de peligro sísmico para Ecuador. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN); 2021. Available from: https://www.igepn.edu.ec/mapas/sismicidad/mapa-peligro-sismico (23.09.2021).
Figure 10. Areas of seismic regions, km2, and their respective percentages in relation to the continental surface of Ecuador based on the non-normative seismic hazard map of the Institute of Geophysics of the National Polytechnic School of Ecuador (IG-EPN, 2021)
Based on the IG-EPN seismic hazard map for a return period of 475 years,7 we calculated the area of seismic regions and their respective percentages in relation to the continental surface of Ecuador, and prepared the map (Figure 10). The analysis of this map shows that 95% of the territory of Ecuador has a PGA > 0.1 g which corresponds to seismic intensities greater than VII [34-36], while regions with seismicity >VIII (ag = 0.2 g) constitute 86%, and 3.8% of the territory of Ecuador has very high seismicity (>IX), where the peak seismic acceleration exceeds 0.5 g.
The analysis carried out in this research shows that the Normative Seismic Hazard Map of Ecuador underestimates the seismic hazard in the Central Andes and in the south-eastern region of the country. For instance, this paper shows that earthquakes up to X-XI intensity have been registered in the Central Andes of Ecuador, with an equivalent PGA above 0.5 g, while the Ecuadorian building standard (NEC-SE-DS 2015) specifies a PGA of 0.30-0.40 g for these zones.
Conclusion
Several scientific works present databases of magnitudes and maps of seismic activity in Ecuador, however, this paper is the first that provides a catalogue of earthquakes with macroseismic intensities greater than VII based on historical and instrumental records from 1900 to 2021. The studied events correspond to earthquakes of very strong and higher intensity levels, according to macroseismic scales MSK-64, MMI or EMS-98. Additionally, we have proposed a series of maps of earthquake epicentres according to intensity, focal depth and magnitudes that allow us to understand the actual effect of Ecuador's seismic activity on buildings and structures. The availability of this information in addition to the seismic hazard is relevant to study the influence of the seismicity of Ecuador on buildings and structures.
The main seismogenic sources in Ecuador are linked to the subduction process of the Nazca plate beneath the South American Plate. However, in this process, the convergence of the Carnegie Ridge, on one hand causes a ploughing effect resulting in shallow-focus earthquakes on the shoreline and deep seismic activity in the Pastaza-Napo region at the Amazon basin, and, on the other hand, the oblique collision of CR generates the northward drift of the NAB, which produces high seismic activity and shallow-focus earthquakes along the Central and Northern Andes.
The shoreline of Ecuador experienced large and great megathrust earthquakes mainly along the northern flank of Carnegie Ridge collision zone. The central and north Andean region of Ecuador shows high crustal activity and registers large historical earthquakes along the CCPP fault system. The sub-Andean zone at the Amazon basin shows an intermediate-depth seismicity in the Pastaza-Napo region and a high shallow-focus activity to the south, between the Macas and Quito-Napo fault systems.
7 Catalogue of earthquakes in Ecuador. Mapa digital interactivo de peligro sísmico para Ecuador. Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN); 2021. Available from: https://www.igepn.edu.ec/mapas/sismicidad/mapa-peligro-sismico (23.09.2021).
The National Seismic Hazard Map of Ecuador underestimate the seismic hazard, mainly in the south-east of Ecuador and in the Central Andes region related to CCPP fault system, where events with macroseismic intensities up to X-XI (PGA > 0.5 g) have been registered. The obtained results suggest that the normative seismic hazard map of Ecuador deserves an actualization.
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