This model covering the Central America and the Caribbean region (CCA) was developed in the framework of the CCARA project (CCARA project) a GEM collaboration project funded by USAID. Cuba and Puerto Rico were included a posteriori by GEM hazard team. During the CCARA project and after it some local organizations and experts were involved and this models benefits of it: University of Costa Rica, Costa Rica - Costa Rican Institute of Electricity, Costa Rica - Nicaraguan Institute of Territorial Studies, Nicaragua - Catholic University of El Salvador, El Salvador - Ministry of Environment and Natural Resources, El Salvador - Panama University, Panama, Puerto Rico Seismic Network, Puerto Rico, National Center for Seismological Research, Cuba. The model was built as a combination of a shallow model, where active faults and distributed seismicity sources were integrated, and a subduction model, divided into its main components (i.e. interface and in-slab). The interface seismicity was modelled using complex faults, while for the in-slab region, the typology of source preferred was the non-parametric source. A publication on the model is currently in preparation.
Information about the OQ model versions and input files can be found on the Results and Dissemination page.
The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.
The Caribbean and Central American region is broadly the Caribbean tectonic plate and vicinity (see Figure 1). The northern and southern margins of the Caribbean plate are characterized by transpressive (mostly strike-slip) faulting between the Caribbean and North and South America, respectively. Bends in the major plate-boundary faults correspond to restraining and releasing zones where deformation is locally more distributed, and in the north, restraining zones are especially important because they form many of the islands of the Greater Antilles and therefore host populations concentrated close to big faults.
Figure 1 - The Central America and the Caribbean Tectonics (modified from Pindell and Kennan, 2009).To the east, oceanic crust of the undifferentiated Americas ocean plate subducts under the Caribbean plate at the Lesser Antilles Trench. The islands of the Lesser Antilles are for the most part volcanoes of this subduction system. Though the evidence for large earthquakes on this subduction zone is poor as the area is under-studied, instrumental seismicity decreases from north to south. The western margin of the Caribbean plate is a subduction zone, the Middle America Trench, where the Nazca ocean plate subducts under the Caribbean. This subduction became oblique near Panama, and a strike-flip fault zone extends along the volcanic arc from Costa Rica through Guatemala, creating localized seismic hazard in populated areas throughout Central America.
This model was created using a compilation of basic databases needed for PSHA (i.e. parametric catalogue, focal mechanisms, active faults, strong motion recordings), which were created following common standards and transparent procedures. These databases were completed mainly by GEM, but the local expert's contribution was crucial.
Earthquake related Catalogues
A homogeneous earthquake catalogue is a fundamental requirement for any seismic hazard analysis. Here, using information from a wide collection of earthquake databases, covering in a different manner the region (see Figure 2), a parametric harmonized catalogue to be used in PSHA calculations was created for the CCA region (Garcia and Poggi. 2017a, see Figure 3). In addition, using information from literature, global datasets (e.g. GCMT, NEIC, ISC) and local seismic networks operating in the CCA region a dataset of focal mechanisms contained 2580 events (3429 solutions) was also compiled (see details in Garcia and Poggi, 2017b).
Figure 2 - Datasets of sources used to create the CCA catalogue: Global coverage: ISC, GEM-ISC, GEM-ISC extended, GCMT; regional coverage: Resis II, CENAIS, PRSN, CDSA and SSNM.
To obtain the CCA catalogue we followed an approach similar to the one used in other GEM models/projects (Weatherill et al., 2016; Garcia et al., 2017; Poggi et al., 2017). It contains 81538 events with 3.0 ≤ Mw ≤ 8.1 from 1502 to 2016 (see Figure 3). This catalogue was then purged from fore- and aftershock sequences and possible seismic swarms, using the Gardner and Knopoff (1974) declustering algorithm and a spatial-time Uhrhammer (1985) window (see details in Characterization and processing of seismic catalogues and/or the references cited above).
Figure 3 - Harmonized earthquake catalogue for the CCA region.
A database of 259 active faults (Figure 4) was created to study the contribution of neotectonic structures to seismic hazard as part of the CCARA project. The database consists in fault traces locations and related attributes describing both, geometry and kinematics (i.e. slip rates, dip angle, etc.). Details about the creation and characterization of the fault can be found in (Styron et al., 2019, under review for Nat. Hazards Earth Syst. Sci). The faults are publicly available on GitHub in a variety of vector formats.
Figure 4 - The GEM active fault database for CCA region. Different colors are used to represent the average deformation style.
Ground Motion Database
Strong motion recordings were collected for the regions of El Salvador and the Lesser Antilles. Data from the Lesser Antilles was retrieved from the Engineering Strong-motion (ESM) website, while the Ministry of the Environment (MARN) provided the recordings for El Salvador in the context of a bilateral collaboration with GEM. A total of 1239 and 600 3-component recordings were collected for El Salvador and the Lesser Antilles, respectively (Figure 5). Events were classified into different tectonic regions based on their locations. For the Lesser Antilles, classification was based on the location of the earthquakes, while for El Salvador classification was provided in the metadata. The stations were assigned Vs30 values. For both El Salvador and the Lesser Antilles, the Vs30 values were estimated from topography since no additional information was available about site conditions.
Figure 5 - The GEM strong ground motion database for CCA region. Events were classified into tectonic region type; INT = subduction interface, SLB = subduction intraslab, ASC = active shallow crust, and UND = undefined.
Seismic Source Characterisation
The Seismic Hazard Model (SHM) was built taking into account the different tectonic settings of the CCA region. It was divided into three main components:
- The shallow seismicity modelled using an integrated model of distributed seismicity (kernel based of gridded point sources) and "simple" crustal fault sources with Mw>6.5;
- The subduction interface seismicity modelled as large "complex" fault sources with a 3D geometry and Mw>6.0;
- The subduction in-slab and deep seismicity modelled as nonparametric ruptures with Mw>6 and depth < 300 km.
Shallow seismicity: Distributed Seismicity
The active shallow hazard component benefits of previous PSHA studies (Benito et al., 2012; Garcia et al., 2003, 2008; Mueller et al., 2003; Bozzoni et al., 2011; Salazar et al., 2014; Wong et al., 2019) and GEM models covering part of the CCA region. To define the distributed seismicity model, initially, the region was discretized into 40 independent source zones (see Figure 6). These areas are represented as polygons (or volumes) delineating regions with homogeneous temporal and spatial characteristics of seismicity, tectonic and kinematic settings. Note that we are including also sources for Colombia and Venezuela.
Figure 6 - Shallow source macro-zonation for the Central America and the Caribbean region.
To characterize the sources the catalogue was our main resource. A sub-catalogue produced by the regionalization procedure was used to derive the parameters characterizing the sources after that declustering and completeness analysis were performed. The parameters characterizing the sources are:
- the maximum magnitude (Mmax, adding an increment of 0.3 to the largest observed event),
- the seismogenic thickness (upper - 0 km - and lower - 40 km - seismogenic depths, constrained using hypocentres of instrumental seismicity and Moho depth definition a a regional scale),
- the focal depth distribution of events and its probability (corresponding to a histogram describing the hypocentral depth distribution from past seismicity),
- the most-likely orientation and faulting styles of ruptures (obtaining using tectonic information and the focal mechanisms distribution),
- the activity rate or magnitude frequency distribution, MFD (represented by a truncated Gutenberg-Richter distribution assuming a magnitude binning of 0.1, a minimum magnitude around Mw4.5; and b and a values computed using the maximum likelihood estimator proposed by Wiechert, (1980).
To model the shallow distributed seismicity, we transformed the area sources described above in a grid of point sources using a smoothed seismicity approach (Frankel, 1995). Smoothed seismicity is modelled similarly to area sources, but rather than using constant a- and b-values, the moment rates are based on observed occurrences. Essentially, we smooth the occurring seismicity onto a grid of points. The advantage of use this approach is the use of larger source zones (see Figure 7), while still capturing spatial variability in seismicity rate. The smoothed seismicity grid (spacing at 0.1°) was obtained by applying a Gaussian filter to each area source declustered sub-catalogue, and computing the fraction of spatial seismicity rates at each grid node. Then, this was combined with the MFD of the source to create a grid of point sources, each of it with its own earthquake occurrence rate. To avoid double counting of seismicity, the MFDs of point sources around fault sources were truncated at MW6.5. A summary of main parameters of shallow/crustal sources is presented in Table 1.
|01||4.97273||1.174||7.50||Cuba intraplate region|
|02||4.28214||0.854||7.37||Swan Islands fault zone|
|03||2.59765||0.626||6.10||Mid-Cayman spreading center|
|04||5.35133||1.094||7.50||Oriente fault system zone|
|07||4.64272||0.985||7.70||North Hispaniola deformed belt zone (Septentrional microplate)|
|12||3.27162||0.828||6.40||Mona Rift zone|
|13||4.37902||1.093||7.50||Los Muertos trough zone (shallow seismicity)|
|14||3.32206||0.925||6.57||Puerto Rico southern zone|
|15||3.24560||0.792||6.57||Puerto Rico northern zone|
|17||5.17624||1.059||7.81||Polochic-Motagua fault system zone|
|18||5.14075||1.045||7.20||Honduras inland extensional zone|
|19||4.90361||1.043||7.00||Depresion de Nicaragua zone|
|20||4.31061||0.799||7.90||Central America Volcanic arc zone|
|21||5.23234||1.088||7.65||Central Costa Rica deformed belt zone|
|22||4.99332||1.036||7.75||Panama microplate/block zone|
|23||4.73501||0.977||7.80||Southern Panama deformed belt|
|24||4.63410||1.023||7.90||Northern Panama deformed belt|
|25||4.37336||0.963||6.40||Shallow seismicity offshore Mexico-Guatemala zone|
|26||4.68727||0.864||7.65||Shallow seismicity offshore El Salvador-Nicaragua zone|
|27||4.87991||1.030||7.52||Shallow seismicity offshore Costa Rica zone|
|28||5.12585||0.907||7.50||Panamá Fracture zone|
|29||4.16454||1.003||6.17||Northern Lesser Antilles deformation front|
|30||3.58910||0.832||6.66||Southern Lesser Antilles deformation front|
|31||5.39022||1.240||7.80||Northern Lesser Antilles volcanic arc zone|
|32||4.64328||1.141||7.80||Southern Lesser Antilles volcanic arc zone|
|33||4.08358||0.996||7.50||Seismicity related to active faults system in the inner arc|
|35||3.29041||0.864||7.69||Northern Venezuela zone|
|36||4.47285||0.960||7.10||"Rigid" area of the Caribbean plate|
|39||4.72758||0.987||6.80||Northern Guatemala-Chiapas zone|
|c00||3.72478||0.860||6.35||Guajira-Paraguana northern Colombia zone (Bonaire block)|
|c01||4.63955||0.896||7.20||Atrato-Murindo suture zone (Choco block)|
|c02||3.73505||0.849||5.71||Triangular Maracaibo (block) zone|
|c03||4.66266||0.938||7.60||Colombian-Venezuelan Piedmont zone|
|c04||4.27833||1.018||6.40||Oca-Ancón fault system zone|
|c05||5.04691||1.092||7.01||Colombian North Andean zone|
|c06||4.28286||0.966||6.55||Caribbean-Colombian northeastern zone|
|v01||4.45622||0.930||7.31||San Sebastian-El Pilar-Costa Norte fault systems zone|
|v02||3.35288||0.795||6.50||Southern Venezuelan (Amazonian) zone|
Table 1 - Seismicity parameters used in the CCA model. The GR a-value is related to the area source.
Shallow seismicity: Crustal fault
Despite of largest crustal destructive events had been associated to active faults, characterization of active faults to be used as source fault into PSHA is a relatively recent development. In addition, several methodologies exist. Here, we are describing the GEM method to build an active fault model from a database of neotectonic active fault as those presented above. This database was created to be used in PSHA, then the faults were characterized (i.e. geometry and kinematic settings) following the OpenQuake standards. Some faults were updated or added recently (e.g. El Salvador, Jamaica, Cuba, on-shore Puerto Rico).
Some assumptions were used to build the model: - The occurrence of the events on the fault follows a double-truncated Gutenberg-Richter (GR) distribution, and the total seismic moment rate from the MDF equals the geological moment rate derived from the fault dimension (area) and slip rate, - The double-truncated distribution is computed using two magnitude extremes bounds (minimum and maximum), then the rates computed above an arbitary magnitude (clipping magnitude) are used, - The a-value of the GR distribution is defined using fault slip rates either measured on the field or inferred by earthquake geologists, - The b-value on the fault is assumed to be equal to those obtained for the area source enclosed the fault (of the major part of it), - The minimum magnitude (lower bound) was arbitrary assumed as Mw4.0, - The maximum magnitude bounding the recurrence model depends on dimensions of the fault's area and was inferred applying Leonard(2010, 2014) scaling relations, - The clipping magnitude (lower bound) was arbitrary assumed as Mw6.5.
In total, we create 241 simple fault sources (see Figure 7a) located in an active shallow crust tectonic regime and comprising the most hazardous structures for inland and offshore areas in the CCA region. Exceptionally, this version of the model do not included fault sources for the Lesser Antilles area where a proper characterization of the faults from a kinematic point of view was not possible this time and it should be included in future versions. The fault sources (trace and surface projection) considered in this version of the CCA model can be also seen in the interactive viewer.
Figure 7a - Fault sources considered for the CCA model (trace and 3d-surface projection).
As explained before, to avoid overlapping contributions from the faults and the background gridded point sources, the activity rates of the point sources around the fault surficial projection was truncated at M~6.5 magnitude (lower bound limit of faults MFD). Following this assumption, earthquakes with M>6.5 can occur on the fault sources (when they are present), otherwise, the area source activity rate prevails. In Figure 7b we presenting an example of this integration for faults located in the northern part of the Hispaniola. The red dashed line (and red points) represent the seismic activity rate for the background (gridded) sources, while the yellow lines are related with contribution of each single fault. The blue line is the total (summed) contribution of the faults. For this particular case, the seismic "productivity" of gridded sources is comparable with those computed using tectonic (faults).
Figure 7b - Comparison of seismic contribution of distributed seismicity and faults located inside an area source for the Polochic-Motagua boundary plate zone.
For this version of the CCA model we are considered five subduction models with sources for Central America, Lesser Antilles and Puerto Rico - Hispaniola regions. A brief description is presented in the next lines.
The Central America model: Most of the Central America countries are located in the north-western corner of the Caribbean Plate (CAR). The western CAR boundary is essentially a subduction zone extended along the Pacific coast from Panama to southern Mexico (Molnar and Sykes, 1969; Hayes et al., 2014, 2018) and tectonically limited by the Middle America Trench (MAT). Here the Cocos Plate (CO) subduct under CAR plate at a convergence rate of 70-90 mm/yr (DeMets et al., 2010; Protti et al., 2012). This caused active volcanism (Central America Volcanic Front, CAVF) and very high seismic activity at shallow and intermediate depth. The Southern Panama Deformed Belt (SPDB) is considered the tectonic boundary between CAR and Nazca plates, while the Polochic-Motagua fault system in Guatemala limited the CAR - North America western plate boundary. Considerable changes of slab shape (dip and orientation) along southern Costa Rica have been recognized by several authors (Trenkamp et al., 2002; Vargas and Mann, 2013), suggesting that Panama, part of Costa Rica and north-western Colombia could be part of a unique block or micro-plate, called Panama microplate . Several destructive events (M>7.5) are reported in historical catalogues and dedicated studies associated to inter -and intra- plate seismogenic sources.
The Puerto Rico - Hispaniola model: The Puerto Rico and Hispaniola (where Haiti and the Dominican Rep. are located) Islands lie close to the northeastern corner of the CAR Plate, where a slow subduction of the North America (NAM) plate beneath the CAR plate take place, dominating the tectonic environment of the region (DeMets et al., 2000, Mann et al., 2002, 2005). The angle between direction of plate motion and and the faults in its boundary help to understand the type of faulting and structural styles, with zones of transpression in southern Cuba, oblique collision between Hispaniola and the Bahama platform, oblique subduction of oceanic crust beneath Puerto Rico and north-western of Hispaniola, and orthogonal (or almost frontal) subduction at the Lesser Antilles islands arc (next subduction model). Given the complexity of tectonic settings, only recently it has been possible to know the rates and directions of interplate motion of CAR plate. DeMets et al. (2000) shows that CAR plate is moving at a rate of ~18 - 20 mm/yr to the east-northeast (070°). In this context the Virgin Islands and Puerto Rico are moving with CAR plate (forming the Puerto Rico - Virgin Islands micro-plate (PRVI) as proposed by Mann et al., 2005), while the Hispaniola moves independently as a detached and complex block of the CAR plate. Jansma and Mattioli (2005) evidenced that differential motion (~5 mm/yr) between PRVI and the Hispaniola is accommodated by slow rifting in the Mona Passage, which separate western Puerto Rico and eastern Hispaniola. The record of large earthquakes and tsunamis in this region is longest and recognized, compilations of historic information reveals that cities as Santiago de Cuba (Cuba), Port-au-Prince (Haiti), Santo Domingo (Dominican Republic), have experienced repeated damaging events in the past (Calais et al., 1998; MacCann, 1985; Doser et al.,2005 among others). Paleoseismology studies in this region (e.g. Prentice et al,. 2003, 2010) reveals that recurrence of major fault ruptures could be estimated in hundreds or thousands of years.
The Lesser Antilles model: The Lesser Antilles are an active volcanic arc created by the subduction of Atlantic oceanic crust beneath the CAR plate (Feuillet et al., 2002, 2010). This "curved" subduction zones extending around 850 km long Lesser Antilles form the eastern margin of the CAR plate, accommodating the ENE motion (~18 - 20 mm/yr) between the NAM and the CAR plates. The seismogenic potential of this subduction has been considered as moderate (Berryman et al., 2015), due that associated largest earthquakes are historical (e.g. 1690 and 1843, M> 7.0) and no M8+ have been reported since 19th century. Some authors considered that it is due to the plate boundary is likely decoupled and convergence is then accommodated mostly aseismically (Stein et al., 1982). This assumption seems to be confirmed by recent geodetic studies (Manaker et al., 2008; Symithe et al., 2015). Nevertheless, this do not preclude the occurrence of a future large event as pointed out by Dorel (1981). The instrumental seismic activity recorded by CDSA is mainly concentrated near islands arc (at 150 - 200 km of the deformation front) and associated to intense volcanism and crustal deformation. The northern sector (above 14°N) is more active than the southern one.
Nazca model: The Nazca subduction model is part of the South America Model (SAM). From SAM we used the two segments (7 and 8), describing the subduction of the Nazca plate in the pacific coast from Northern Ecuador to Southern Panama. Details about this model can be found in the documentation related with the SAM model.
North Panamá Deformed Belt model: The North Panamá Deformed Belt (NPDB) is the northern limit of the Panamá microplate. NPDB extends offshore the Caribbean coast of Panamá from the north-western border of Panamá and Colombia to Puerto Limón in Costa Rica. Its origin is related with the convergence between the Caribbean plate and the Panamá microplate. On this overthrust fault reverse faulting predominant and on-shore and off-shore deformation with a SW-dipping is confirmed by instrumental seismicity recorded by regional and local networks (Camacho et al. 2010) as well as historical large events (e.g. 1882 Panama Mw7.9 event, Camacho and Víquez, 1993). Alvarado et al. (2016) suggest a variation of tectonic regime from Panama (shallow subduction) to Costa Rica (typical thrust fault system).
"Los Muertos" Trough model: The Muertos trough a ~650 km-long deformed belt bound the Puerto Rico microplate at south of the Dominican Republic (DR) and Puerto Rico (Mann et al. 2005). It is considered as a active subduction zone (Dolan et al. 1998; LaForge and McCann, 2005; McCann, 2007) accomodating the closure between the Caribbean plate and the Puerto Rico microplate. However, Granja Bruña et al., 2010 interpreted this zone as a retroarc thrusting using gravity modeling. The westermost limit of this deformed belt is close to the Beata fault in DR and dieng out gradually to the east transferring the plate motion to faults in the Anegada trough. The distribution of seismicity is difuse and have a high degree of uncertainty. This make the definition of the plate geometry a challenge (Granja Bruña et al., 2010). However, the Muertos Trough plays an important role in the tectonic of the north-eastern Caribbean plate boundary and a source zone has been created for this version of the CCA model.
The methodology utilized follows a new approach developed within the CCARA project and currently tested (and improved) in a number of different subduction areas across the world (Pagani et al., in preparation). The approach is divided in two main steps: the first one aiming at defining the geometry (e.g. top and bottom of the slab, average thickness of slab) and the structure of subduction including its possible segmentation, the second one is focused on seismic activity rate characterization of subduction sources. The starting point for the definition of the subduction geometry is the creation of a number of manually digitized profiles describing the contact between the subducted slab and the overrinding plate to define a 3D meshed surface. The profiles were obtained using cross sections along trench axis. The data plotted on the cross sections (see example in Figure 8) is meant to illuminate the subsurface subduction structures and tectonic processes that contribute to seismic hazard. The data used was:
- Best located hypocentres (CCA catalogue),
- Centroid moment tensors (CMTs) from the Global CMT project (Dziewonski et al., 1981; Ekstrom et al., 2012),
- Moho depth estimates from Lithos1.0 (Pasyanos et al., 2014) and Crust1.0 (Laske et al., 2013) models,
- Slab depth estimates from Slab2.0 (Hayes et al., 2018)
- Shuttle Radar Topography Mission (SRTM) topography (Farr, 2007)
- General Bathymetric Charts of the Ocean (GEBCO) bathymetry (Weatherall et al., 2015)
Figure 8 - Example of cross-section describing the contact between the subducted slab and the overrinding plate.
Figure 9 - Example of 3D volume representing the portion of the subduction generating in-slab sesimicity for Central America - Mexico subduction.
We model the geometry of subduction interface sources as Openquake complex faults and float possible ruptures (ranging specified magnitude limits from the MDF and with a given rupture aspect ratio) across the meshed surface obtained. To determinate the limits of the interface sources (i.e. portion of the contact between the slab and the overlying plate, usually considered locked) we cut the 3D mesh at two depths: 10/15 km and 40/50 km. For in-slab seismicity we used non-parametric ruptures sources. Our algorithm models ruptures at grid of points throughout the meshed approximation of the slab volume, and keeps ruptures that fit within the slab. The geometry of the ruptures with normal slip and dipping 45° and 135° is defined within a volume constrained at the top (below interface lower depth definition) and at the bottom by a surface obtained by projecting the in-slab-top surface 60 km toward a perpendicular direction (see Figure 9).
For the characterization of earthquake occurrence, we used a regionalized sub-catalogue generated for a specific tectonic region (e.g. Central America interface). We performed the declustering (using Uhrhammer, 1986 windowing) and completeness analysis and estimate the occurrence rates following a double truncated Gutenberg-Richter MDF as for the shallow distributed seismicity model. The lower bound of interface MDFs is arbitrary fixed at Mw6.0 for all interface sources and at Mw6.5 for the in-slab ones. The upper bound of the MFD for interface sources was defined combining information on past seismicity and constraints from the subduction geometry and a magnitude-scaling relationship (Strasser et al., 2009), while for the in-slab sources the rates were distributed among the computed non-parametric ruptures.
The GEM Subduction Toolkit was used to build all models. The geometry of the sources is presented in Figure 10 (superficial projection of complex faults characterizing interface seismicity) and Figure 11 (top of surface enveloping the non-parametric sources).
Figure 10 - Complex faults (surface projection) characterizing the interface seismicity for the CCA region/model. CAM: the Central America model, PAN: the North Panamá Deformed Belt model, LAN: the Lesser Antilles model, PRC: the Puerto Rico - Hispaniola model and LMT: "Los Muertos" Trough model.
Figure 11 - Top of surface envelop the in-slab non-parametric sources included in the CCA model. CAM: Central America model, LAN: the Lesser Antilles model and PRC: the Puerto Rico - Hispaniola model.
In Table 2. we summarize the parameters characterizing the sources.
|int_cam||6.78781||1.084372||8.50||Interface source for the Central America subduction model|
|int_lan||4.706386||0.919454||8.50||Interface source for the Lesser Antilles subduction model|
|int_prc||5.347351||1.041906||8.50||Interface source for the Puerto Rico-Hispaniola subduction model|
|int_lmt||3.158115||0.720279||7.75||Seismicity related with "Los Muertos" fault system|
|int_pan||3.7579408||0.818074||8.25||Seismicity related with North Panamá Deformed Belt|
|slab_cam||6.123138||1.014256||8.50||In-slab seismicity characterization of the Central America subduction model|
|slab_lan||4.509280||0.863988||8.50||In-slab seismicity characterization of the Lesser Antilles subduction model|
|slab_prc||4.228295||0.864203||8.00||In-slab seismicity characterization of the Puerto Rico-Hispaniola subduction model|
Table 2 - Seismicity parameters used in the CCA subduction models..
Ground Motion Characterization
The GMPE selection process for CCA involved three main steps. First, we pre-selected a set of about 10 candidate GMPEs from the literature for each tectonic region considered in the SSM. The pre-selection was performed using a subset of the well-established exclusion criteria proposed by Cotton et al (2006) and Bommer et al. (2010). This was followed by a comparison of the ground motion scaling of the pre-selected GMPEs using a suite of rupture scenarios consistent with the ruptures modelled in the seismic source model. Such comparisons (referred to as trellis plots) allowed for identifying and excluding GMPEs that behave unfavourably, for example during extrapolation outside the suggested applicability range. The final step of the selection process involved comparison between the ground motions computed by the pre-selected GMPEs and the ground motions observed in the region. Data-to-model comparisons were performed by analysing the ground motion residuals (e.g. Scherbaum et al., 2004; Stafford et al., 2008) using the OpenQuake strong motion toolkit (Weatherill, 2014).
For the final selection we tried to achieve balance by selecting models that both over and underpredict the observed ground motions in each of the tectonic regions when possible, according to the results of the residual analysis. Two notable results of the residual analysis were the observation of lower ground motions for crustal events than expected in both the Lesser Antilles and El Salvador, and differences in attenuation for intraslab earthquakes in the Lesser Antilles and El Salvador. The final GMPE logic tree is shown in Table 3. The GMPEs selected for active shallow crust and subduction interface are the same for the Lesser Antilles and El Salvador, while for subduction intraslab they are different. Hence the logic tree distinguishes between four main tectonic regions: Active Shallow Crust, Subduction Interface, Subduction IntraSlab (referred to Panama - Mexico subduction), and Subduction IntraSlab LAN_PRC, while sources in Colombia Subduction Interface COL Subduction IntraSlab COL use the GMPEs selected with the SARA project.
|Subduction Interface COL||Weight|
|Subduction IntraSlab LAN-PRC||Weight|
|Subduction IntraSlab COL||Weight|
|Active Shallow Crust||Weight|
Table 3 - GMPEs used in the CCA model.
For this version of the model, only the epistemic uncertainty related with Ground Motion characterization was considered (combination of three GMPEs for each tectonic environment). The model consists in a source model and 27 end-branches. In future versions, epistemic uncertainty related to Seismic Source (i.e. alternative fault model, segmented subduction model) will be considered too.
Hazard curves were computed with the OQ engine for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s. The computation was performed on a grid of 28914 sites (spaced at approximately 10 km) with reference site conditions with shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s.
The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.
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