The current state of seismic monitoring in Puerto Rico
John F. Clinton1, Georgia Cua2, Víctor Huérfano2, Christa G. von HillebrandtAndrade2, José Martínez Cruzado1
A. Introduction
The US Commonwealth of Puerto Rico has a population of 3.8 million (2000
Census), which amounts to a higher population density than any US state. The island,
approximately 160km from east to west by 50km from north to south, is bounded by offshore active faults on all sides. Numerous local and regional events in the recorded
history with M>7.0, some of which have generated tsunamis, have caused extensive
damage to local infrastructure; the last significant ground motions were felt on-shore in
1918. The USGS hazard maps (Mueller et al,, 2003) indicate that the seismic hazard is
similar to the Basin and Range province in the Western USA, and the island is assigned
Seismic Zone 3 in the current standard Building Code in Puerto Rico, the 1997 UBC. The
significant hazard, combined with the large population and untested infrastructure, result
in a potentially devastating combination for Puerto Rico. Efficient emergency response in
the event of a large earthquake will be crucial to minimising the resultant loss of human
life and disruption of lifeline systems. The first step in providing an appropriate response
to such a disaster is a timely knowledge of the magnitude, location and expected ground
shaking and damage patterns from the event. This requires a modern and dense seismic
network, capable not only of recording the earthquake ground motion without saturation,
but also doing so in real-time and then providing data for near-immediate analysis, which
can be made available to the emergency services and community at large.
The seismicity of the island, as well as the northeastern Caribbean region in general
(including the US and British Virgin Islands), is monitored jointly by the Puerto Rico
Seismic Network (PRSN) and the Puerto Rico Strong Motion Program (PRSMP), both
1
Puerto Rico Strong Motion Program, Department of Civil Engineering and Surveying,
University of Puerto Rico at Mayagüez
2
Puerto Rico Seismic Network, Geology Department, University of Puerto Rico at
Mayagüez
1
operating within the University of Puerto Rico at Mayagüez. They currently acquire,
analyse and archive broadband, short period and strong motion seismic data in
continuous real-time format, using both Antelope and Earthworm software, from stations
on Puerto Rico, surrounding islands, the US and British Virgin Islands, and the
Dominican Republic. In addition, PRSN imports and processes data from various
regional stations operated by other networks. The PRSMP also operates some dial-up and
stand-alone installations. Stations range from state-of-the-art seismic vaults for event
locations and magnitude determination, to free-field and structural installations for
engineering studies and structural health monitoring. In the near future, the networks
expect to add continuous streams of data from tidal gauges and buoys (for tsumani
warning), GPS and digital weather stations to their operations.
B. Tectonic background
The island of Puerto Rico has a long history of damaging earthquakes and
tsunamis. The island is bounded on all sides by major tectonic fault lines (Figure 1).
Major earthquakes have produced damaging ground motions in Puerto Rico in 1615,
1670, 1751, 1776, 1787 (~M8.0 Puerto Rico Trench), 1867 (~M7.3 Anegada Passage)
and 1918 (~M7.3 Mona Passage). Large events also occurred in 1943 (~M7.5) and 1946
(~M7.8) that caused much damage in the neighbouring Dominican Republic (PRSN
Historical Catalogue, http://temblor.uprm.edu/~victor/PRSN/history/; Shepherd and
Lynch, 1992). The 1867 and 1918 events were accompanied by destructive tsunamis
(Mueller et al, 2003; Reid and Taber, 1919).
Puerto Rico is located on a microplate sandwiched between the obliquely subducting
North American and Caribbean plates (Figure 1). Puerto Rico accommodates
approximately 16.9mm/yr of deformation relative to North America, and 2.4mm/yr
relative to the Caribbean plate (Jansma and Mattioli, 2005; Jansma et al., 2000), primarily
by left-lateral strike-slip motion along east-west striking faults. The main sources of
seismic activity in the region are at the supposed boundaries of the microplate; the
subduction zones to the north (the Puerto Rico Trench, which is the location of the largest
gravity anomaly on earth) and south (the Muertos Trough), and zones of extension at the
2
Anegada Trough to the east, and the Mona Canyon region to the west. All regions are
capable of producing events greater than M7.0, and all have evidence of having done so
in the recorded history of the island (Ascencio, 1980; Moya and McCann, 1992; Macari,
1994). On average Puerto Rico is strongly shaken with Modified Mercalli Intensity
(MMI) >VII once every hundred years, and MMI > VI is experienced on the island once
every 50years.
In addition to these off-shore sources, recent trenching shows evidence of 2 surfacerupturing events on the inland South Lajas fault in southwestern Puerto Rico (Prentice et
al., 2000, Prentice and Mann, 2005), predominantly along a normal fault with a
component of strike-slip motion, both within the last 5000yr. This 50-km long inland
fault segment can produce M7.0 events (LaForge and McCann, 2003), and potentially
could be part of a longer fault zone that extends towards Ponce, the second largest city on
the island (population 186,000, 2000 Census). Other shallow faults, mainly with E-W
trends, are interspersed across the island. These include the Great Northern and Southern
Puerto Rico Fault Zones. These structures have unknown potential for large magnitude
events, as yet there is no evidence of Holocene rupture. Tectonic models (Prentice and
Mann, 2005) and GPS studies (Jansma and Mattioli, 2005) indicate there are active faults
on-shore to accommodate some extension across the island.
The most recent large event to cause widespread damage across the island occurred in the
Mona Passage in 1918, with MS7,3 (Pacheco and Sykes, 1992). This event caused
substantial structural damage to the large towns of Mayagüez and Aguadilla on the West
of the island. The associated tsunami had a run-up of 6m at Aguadilla, and 2m at
Mayagüez (reaching over 1km inland) (Mercado and McCann, 1998), which killed over
100 people. Widespread liquefaction was observed along the unconsolidated floodplains
in the municipalities of Añasco and Mayagüez (Capacete et al., 1972; Moya and
McCann, 1992), areas now with pockets of dense population. With the island in general
now having a far greater density of population and infrastructure – infrastructure that has
island-wide not yet been tested by strong motions since this event in 1918 – a repeat of
such grounds motions would lead to a far more severe loss of life and infrastructure.
3
The tsunami risk in the north-east Caribbean is also very real. Aside from the potential
for large magnitude events (Huérfano, 2003), recent bathymetry studies have shown
numerous large landslide scarps and cliffs near the Puerto Rico Trench as well as the
Muertos Trough (Grindlay et al., 2005a; Grindlay et al., 2005b; ten Brink, 2004). The
off-shore bathymetry is particularly severe to the North of the island, where the Puerto
Rico Trench drops to a depth of over 8.3 km just 180 km north of the island. The interior
of the island is mountainous; resulting in much of the population being concentrated in
the at-risk low-lying coastal flood plains and alluvial basins.
C. Seismic Networks in Puerto Rico
The Puerto Rico Seismic Network (PRSN) and the Puerto Rico Strong Motion
Program (PRSMP), jointly monitor seismic activity in the northeastern Caribbean region.
The primary duty of the PRSN is to identify and provide information on local, regional,
and teleseismic earthquakes. PRSN is also the host of the Emergent Tsunami Warning
System for Puerto Rico and the Virgin Islands. PRSN is the reporting authority for event
locations and magnitudes, and maintains the authoritative event catalogue. PRSN operate
vault stations primarily in low noise locations. The objective of the PRSMP is to record
on scale ground motions from earthquakes affecting the island with as high a quality and
station density as possible. The PRSMP maintain a dense urban network with both freefield stations and structural arrays. Both networks share the common goal of providing
high-quality data and information in response to needs of the emergency management,
engineering, and scientific communities, as well as the general public.
PRSMP and PRSN run complimentary operations and share all continuous data in realtime (see Figure 2). This exchange provides an essential level of redundancy and
robustness that will be important in ensuring timely and accurate information following a
large earthquake.
4
D. Puerto Rico Seismic Network (PRSN)
The Puerto Rico Seismic Network (PRSN) has historically provided locations and
magnitudes for earthquakes in the Puerto Rico and Virgin Islands (PRVI) region. PRSN
is the reporting authority for the region bounded by latitudes 17.0N to 20.0N, and
longitudes 63.5W to 69.0W (Figure 1). The network has been operating since 1974, when
the U.S. Geological Survey installed several short-period stations for the Puerto Rico
Electric Power Authority that were used to evaluate local seismicity in response to
concerns regarding the planned construction of two nuclear power plants. In 1982, the
network was transferred to the University of Puerto Rico at Mayagüez, where it has been
operating under the jurisdiction of the Department of Geology since 1987.
The main objective of the PRSN is to record, process, analyze, provide information and
research local, regional and teleseismic earthquakes, providing high quality data and
information in order to be able to respond to the needs of the emergency management,
academic and research communities, and the general public. It presently operates 13
broadband stations and 10 short period stations throughout Puerto Rico and the US and
British Virgin Islands (Figure 3). 6 of these broadband stations also jointly house strong
motion sensors. The broadband (BB) stations consist of Guralp CMG 40T, CMG 3 ESP
and CMG 3T seismometers recording onto 24-bit Refraction Technology (130 and 72A),
NetDas DAQ or Quanterra Q330 digitizers, all sampling at 40 sps. The strong motion
(SM) sensors are all Kinemetrics EpiSensors, sampling at 100 sps. The broadband
sensors are linked to the central data collection center in Mayagüez via Monitron UHF
digital radios, DDS 56K telephone lines, spread-spectrum radios and Internet service. The
analogue short period (SP) seismic stations consist of Teledyne S-13 and Mark L-4
seismometers and the data is digitized at 16-bits at 100 sps at the offices of the PRSN.
The PRSN runs Earthworm software (Johnson, et al, 1995) to acquire and write
waveforms to disk for permanent archival. Automatic locations and alerts are generated
for events in Puerto Rico, the Intra America Seas, and the Atlantic by the EarlyBird
system (Whitmore and Sokolowski, 2002), which monitors PRSN stations as well as
5
some 30 other ‘virtual’ stations operating in the North, Central and South America and
other sites in the Caribbean (Figure 2). Manual locations and analyst review of automatic
locations of events within the PRSN area of responsibility (AOR) is facilitated by the
PRDANIS (Puerto Rico Data Analysis and Information System) software developed by
PRSN using the broadband, strong motion and short period waveforms. The location
algorithm is based on the inversion schema HYPOINVERSE-2000 (Klein, 2002), using
the crustal model of Huérfano and Bataille (1994). Currently all magnitudes reported by
PRDANIS are Md, duration magnitude. All phase arrival times, locations, amplitudes and
magnitudes are reviewed by a seismic analyst, usually on the same day, and always
within one week. The continuous waveform data is permanently archived at PRSN in
GSE2.1 format, though all broadband waveforms are continuously exported to, and
archived in SEED format at IRIS (Incorporated Research Institutions for Seismology,
http://www.iris.edu). Full dataless SEED volumes are available for all stations. Phase
data is saved in HypoInverse 2000 format.
PRSN hosts a website with a searchable event database, felt event reports and general
information about seismicity in the area of responsibility, which can be accessed from
http://redsismica.uprm.edu/english/.
PRSN is also producing ShakeMaps (Wald et al., 2000) for all felt events in Puerto Rico
and the Virgin Islands, and provides QDDS (Quake Data Distribution System) data to the
USGS ‘Did You Feel It?’ tool (http://pasadena.wr.usgs.gov/shake/prt/).
E. Puerto Rico Strong Motion Program (PRSMP)
Strong motion instrumentation efforts in Puerto Rico began in the 1970’s and
have continued at a steady pace due to the activities of the Puerto Rico Strong Motion
Program (PRSMP). In the immediate aftermath of a large earthquake, the mission of the
PRSMP is to provide timely information regarding the distribution of peak ground
shaking to emergency management officials to guide response and recovery efforts. In
general, the PRSMP aims to provide the best strong motion data to the scientific and
engineering communities to improve land use and construction of earthquake-resistant
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structures. The PRSMP focuses on (1) deploying and maintaining instrumentation for
recording large earthquakes that will produce damaging ground motions on the island
with as high a data quality and station density as possible; (2) providing timely and
appropriate information to the local authorities, seismologists and engineers; and (3)
supporting and conducting research activities associated with these records, in particular
the understanding of the effects of earthquakes in Puerto Rico, and the mitigation of
potential damage from future earthquakes.
Currently the PRSMP maintains a network of (1) 78 3-component 18-bit ETNA urban
free-field stations; (2) 6 24-bit EpiSensors alongside broadband sensors (jointly operated
with the PRSN) at remote sites with vault conditions, and (3) 8 monitored structures with
multi channel 19-bit K2 instrumentation (Figure 4). The density of strong motion
instrumentation across the island is comparable to Greater Los Angeles, and greatly
exceeds the density deployed in California as a whole.
Station sites for the urban free-field network are selected based on the proximity to highly
populated urban areas and regions of high seismicity (i.e. regions exposed to the greatest
seismic risk). In addition, local cultural noise, site geology, ease of access for
maintenance, availability of internet or telephone lines, and security are all important
considerations. Of the 78 stations, 9 have a real-time continuous internet communication
with PRSMP. These internet stations are primarily located on different University of
Puerto Rico campuses throughout the island. Of the remaining ETNA stations, 42 have
dial-up telephone communications, and 27 have no communications (‘standalone’
stations, and must be visited to gather data). For reasons of accessibility, security, and
ease of obtaining site permissions, a majority of the dial-up and standalone stations are
installed in fire stations or on Catholic church property.
In addition to the ETNA stations, PRSMP monitors 8 structures across the island with
multi-channel sensors. These sites are all equipped with 19-bit Kinemetrics K2
dataloggers and Kinemetrics EpiSensors or FBA-23/FBA-11 sensors. The critical
infrastructures monitored are: high rise buildings (Plaza Immaculada Apartment Complex
7
and Minillas Government Center, San Juan), concrete dams (Lucchetti, La Plata and
Carraizo), and bridges (Ponce Bypass, Mayagüez Viaduct, Paso del Indio bridge). All
structural installations are currently stand alone.
The PRSMP also shares the operation and maintenance of the 6 strong motion sensors colocated with PRSN broadband sensors (Figure 3), ensuring the entire seismic frequency
and amplitude bandwidth is covered at these select stations
The Antelope Real-Time System (ARTS, http://www.brtt.com/; Pavlis et al., 2005;
Malone, 2000) facilitates communication with the PRSMP ETNA stations as well as with
the strong motion and other data collected at PRSN. Antelope software also provides
automatic and reviewed location and magnitude determinations (Richter Magnitude (M L)
for local events; Body Wave Magnitude (mb), and Surface Wave Magnitude (MS) for
regional and teleseismic events), which run as backup to PRSN operations. All data is
archived in a temporary ring buffer of 15 days in SEED format, with permanent archiving
of all data from all triggered events in SAC format. Event information, and selected event
data, is available on-line at http://www.uprm.edu/prsmp.
Data from 10 strong motion stations which recorded the recent 3 march 2006 Md5.3 event
off Anegada was submitted to Cosmos, and is available from the their website
(http://db.cosmos-eq.org/).
F. Brief Description of the PRSN Catalogue
The PRSN generates and maintains the earthquake catalogue for Puerto Rico and the
Virgin Islands. Prior to July 2004, the PRSN catalogue was compiled using the PRHYPO earthquake location code with both local (Richter Magnitude, ML) and duration
magnitude (Md) computed using the equations of von Hillebrandt and Bataille (1994). In
July 2004, the location schema HYPOINVERSE2K was implemented and magnitudes
have been calculated from short period and broadband data using the Eaton (1992) “full
digital velocity” equations. PRSN have also introduced near-real time moment magnitude
8
estimation based on a Regional Moment Tensor (RMT) inversion code (Randall et al.,
1995) and the ASPO search grid algorithm of Zahradnick et al. (2001).
Figure 5 shows the epicenters of the analyst-reviewed events in the PRSN local reporting
region (AOR) between January 1986 and March 2006. There are over 14,100 events in
the catalogue, 9 with M>5.0. The largest event was an Md5.6, occurring at 67km depth,
just south of Anegada, BVI, on 7 December 1998. The most recent large event was an
Md5.3 event 80km NE of Anegada, on 3 March 2006. Shallow seismicity is concentrated
in regions along the Mona Canyon, the region between the Puerto Rican Trench and the
19o N fault zone, the Sombrero fault zone, and on-land across the south of Puerto Rico.
The oblique subduction of the North American Plate under the Puerto Rican microplate
appears to be the source of much of the deep seismicity. The density of seismicity is
shown in Figure 6. The seismicity is dominated by 3 regions; 2 to the North of the island,
near the Puerto Rico Trench, and another in the southwest of the island, near Cabo Rojo.
Huérfano et al. (2005) suggest the increased seismicity in SW Puerto Rico may be due to
local topographic effects.
Short period sensors dominated the network until 2000, when broadband sensors were
first introduced, though the station density has remained relatively constant. Figure 7(a)
shows the number of events binned into periods of 3 months. It is clear that the level of
recorded seismicity increased by about 20% once the broadband sensors were introduced
to the network. The spike in events in the bin from January-March 2006 is due to the
M5.3 indicated in Figure 5. This anomalously large number of events reflects significant
recent improvements in automated event-picking algorithms using both Earthworm and
Antelope modules. In Figure 7(b) and 7(c), the magnitude and depth distribution of the
catalogue is analysed. From Fig. 7(b), the average magnitude of completeness, M C, for
the entire catalogue can be estimated to be about Md 3.3. The majority of events are
shallow (Figure 7(c)), though the spike in event depth at 25km is due to this being the
initial default depth for events up until 2004. Figure 7(d) shows the Gutenberg-Richter
distribution for the catalogue, with a b-value of 1.12.
9
The spatial distribution of magnitude of completeness for the catalogue across the PRSN
reporting region is shown in Figure 8. At best, the magnitude of completeness is Md2.4,
and is at least Md3.0 across the island of Puerto Rico. At the most distant areas from land,
(and thus most distant from stations), the magnitude of completeness degrades to over
Md4.2. This degradation is an unavoidable consequence of the island geography, but the
problem is significantly compounded by the frequent loss of communication with the
most remote sites: the Virgin Islands to the east, and Desecheo and Mona Islands to the
west of Puerto Rico. The ongoing efforts to secure high quality broadband data with good
communications at the more isolated sites, such as Anegada and Mona, coupled with
expected installations in the Dominican Republic, will reduce the magnitude of
completeness in the extreme regions.
In addition to the difficulties is detecting off-shore events, exact earthquake location is
also difficult in the region as most of the stations lie in a band between 18oN and 18.5oN,
with poor azimuthal constraint on events lying to the north and south (Mendoza and
Huérfano, 2005).
G. Current Network Initiatives
1. ShakeMap for Puerto Rico
ShakeMaps are ground shaking and intensity maps that combine instrumental
measurements of shaking with information regarding local geology and earthquake
location and magnitude to estimate shaking variations throughout a geographic area
(Wald et al., 2005). The ShakeMap software is distributed and maintained by the USGS,
with local network operators responsible for customizing the distributed software to their
particular network environment. The PRSN has the capability to manually generate
ShakeMaps within 1.5 hours following a significant felt event. An example for the recent
2 March 2006 M5.3 event in the Lesser Antilles is shown in Figure 9. PRSN ShakeMaps
are constrained by peak ground motion parameters obtained from real-time broadband
and strong motion instruments operated by PRSN and PRSMP; the initial ShakeMaps can
be updated as strong motion data from PRSMP dial-up stations become available. Site
amplification effects are approximated by assigning Vs30 values on a uniformly-spaced
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1.5 km grid throughout the island. A set of 14 Vs30 measurements (Odum et al., 2006)
sampling representative geologic units throughout mainland Puerto Rico was used to
determine how to assign average Vs30 values to geologic units.
The efficiency and performance of the ShakeMap system in Puerto Rico can be improved
by: 1) automating the transfer of data from the PRSN earthworm data acquisition system
to ShakeMap, 2) updating the current site conditions map to take into account detailed
microzonation studies available for the San Juan Metropolitan Area (Aponte et al., 2000),
Ponce, and Mayaguez (Llavona, 2004), the three largest urban centers on the island, and
3) educating potential users on how to use ShakeMap products to guide post-earthquake
response and recovery efforts.
2. Focal Mechanisms and Moment Tensors
With the support of SeaGrant, the PRSN is evaluating the use of available seismological
methods for the rapid identification of earthquake source parameters using the broadband
seismic waveforms recorded by the Puerto Rico Seismic Network and to develop
automated procedures for the emergent Tsunami Warning System in the Puerto RicoVirgin Islands (PRVI) region. This work involves an evaluation of seismologic methods
of waveform analysis using local and regional earthquake data recorded by the PRSN and
a subsequent adaptation of these seismologic methods in numerical procedures that can
be implemented rapidly within the PRSN seismic-detection and information system. The
results will be incorporated to the broadcast schemas as part of the tsunami protocol in
the PR-VI region
The implementation of near-real time moment magnitude estimation based on the
Regional Moment Tensor (RMT) inversion code of Randall et al. (1995), and regular
calculation of first motion focal mechanisms are products of this work. For the recent 2
March 2005 (25km deep), a moment magnitude of MW5.5 was determined within 1 hour
of event initiation. The focal mechanism has a strike/dip/rake of 83.2o/52.4o/53.6o, a
thrust fault with some strike-slip component reflecting the compression dynamics typical
of subduction zones, and is likely be related with the plate interface. This is consistent
11
with
the
Harvard
Quick
CMT
solution
(http://www.seismology.harvard.edu/CMTsearch.html), which indicates an MW5.5 high
angle thrust event with strike 103o.
3. Structural Monitoring
PRSMP currently monitors 8 structures, all stand-alone, with multi-channel K2 systems,
with ETNA free-field sensors. These are all located on critical infrastructure around the
island; 2 high rise buildings in San Juan, 3 bridges on the main road around the island,
and 3 concrete dams. The instrumentation is summarised in Table 1.
Currently all these stations are standalone, though cable internet is being installed at the
Plaza Inmaculada building. 9 of the 15 channels will be continuously monitored at
PRSMP, with the natural frequencies and modes of the building being monitored to
investigate whether there are significant changes in the dynamic properties of the system
during earthquakes or hurricanes that could indicate potential structural damage (Clinton,
2004; Clinton et al, 2006).
The PRSMP is also in the process of installing dense instrumentation at the 19-story El
Castillo apartment complex in Mayagüez, a component of the Advanced National
Seismic System (ANSS) Structural Response Monitoring System. This test-bed will
consist of at least 27 channels of 24-bit strong motion data recording on Quanterra Q330
dataloggers.
4. Network Expansion and Improvement

Upgrade at remote sites and new installations
Existing infrastructure at Mona Island in Puerto Rico and Anegada in the British Virgin
Islands (Figures 1, 3) will be upgraded by installing 24-bit broadband and strong motion
sensors and dataloggers. Satellite telemetry will be used to transfer data to PRSN. Both
of these stations will also provide data to the emergent USGS Earthquake and Tsunami
Monitoring System for the Caribbean. In addition, the currently non-operational short
12
period station at CSB (Figure 3) is likely to be moved to an area near San Juan, which
will improve the sensitivity of the network in the NE region of the island.

Installations in the Eastern Dominican Republic
Two sites have been selected and permitted in the Eastern Dominican Republic, at
Samana and Punta Cana (Figure 1), where the PRSN and PRSMP will jointly install and
operate 24-bit collocated broadband and strong motion stations, with real-time
continuous internet data transmission.

Strong Motion Monitoring in the British Virgin Islands
The PRSMP has begun a 3-year contract with the Department of Disaster Management in
the British Virgin Islands to install a suite of free-field and structural strong motion
sensors at critical local infrastructure. The airport control tower on Beef Island and the 3story Government Building in Road Town, Tortola will have 12-channel K2
instrumentation with both free-field and structural sensors. Both lie on reclaimed fill.
Free field sites on hard rock in Road Town on Tortola, and Spanish Town on Virgin
Gorda are in the course of being instrumented. All instrumentation will be transmitted in
real time to PRSMP.
Acknowledgements
We would like to thank the PRSN and PRSMP personnel, technicians, administrative
staff and students, who have made immense contributions to the success of both
networks. The figures in this paper were made with the Generic Mapping Tools (GMT)
software (Wessel and Smith, 1991), and ZMAP (Wiemer, 2001). The authors gratefully
acknowledge GNU software developers. Funding for work on Moment Tensors at PRSN
was provided by the SeaGrant Program (R-122-2-04).
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17
Figure 1: Map of northeast Caribbean, showing major tectonic structures and
approximate locations for damaging earthquakes in recent history. GPS
displacement vectors are from Jansma et al. (2000). [USVI: US Virgin Islands; BVI:
British Virgin Islands; Cul: Culebra, PR; Vq: Vieques, PR; PC: Punta Cana; SM:
Samana; SLF: South Lajas Fault; GSPRFZ: Great Southern Puerto Rico Fault
Zone; GNPRFZ: Great Northern Puerto Rico Fault Zone]
18
FIGURE 2: Data Acquisition and Processing at PRSN / PRSMP
19
FIGURE 3: Stations with real-time continuous monitoring at PRSN. All are
operated by PRSN except the IRIS station SJG and the PRSMP 18-bit strong
motion stations. 3 joint BB and SM stations will be installed in locations
outside the map: on Mona Island, and at Punta Cana and Samana in the
Dominican Republic (see Fig 1). Currently short period stations IDE and CSB
are out of operation. [BB: broadband sensor; SM: strong motion sensor]
20
FIGURE 4: Strong Motion stations in Puerto Rico monitored by PRSMP.
Additional details of the dense instrumentation in three largest towns in Puerto
Rico, San Juan, Ponce and Mayagüez, is shown.
21
FIGURE 5: Seismicity within PRSN local reporting region between January 1986
and March 2006. The largest event in this time period was a M5.6 located near
Anegada, BVI. There were 9 events with M>5.0 (yellow stars). The most recent large
event was a M5.3 on 2 March 2006, with cropped text at upper right of map.
22
Figure 6: Density of seismicity in the reporting region, PRSN catalogue, Jan1986Mar2006. Local seismicity is concentrated in southwest Puerto Rico (south of the
Great Southern Puerto Rico Fault Zone); the region between the Puerto Rico trench
and the 19o Fault Zone; and the Sombrero seismic zone (see Figure 1 for fault
locations).
23
(a)
(b)
(c)
(d)
Figure 7: Analysis of the PRSN Catalogue (Jan 1986 - March 2006) (a) number of
events over time (3month bins); (b) number of events in 0.1 magnitude bins; (c)
number of events in 5km depth bins; (d) Gutenberg-Richter relation.
24
Figure 8: Geographical distribution of the magnitude of completeness, MC, for the
PRSN Catalogue for the reporting region (Jan 1986 – Mar 2006). MC is Md2.5 for a
significant portion of the center and southwest of the island, and is at least Md3.0
throughout the island of Puerto Rico. As distance from the islands increases, the
magnitude of completeness degrades, in some regions being greater than Md4.0.
25
Figure 9: ShakeMap for a 2 March 2006 M5.3 event located in Sombrero Seismic
Zone (see Figure 5 for location).
26
Structure
Name
Location
San Juan
Station
ID
B02L
Etna
Free field
SJ05
# K2
sensors
15
High Rise Apartment
Plaza Inmaculada
High Rise Building
Highway Overpass
Minillas Government
Center
Mayagüez Viaduct
San Juan
B01L
SJ05
6
Mayagüez
B01R
MY09
24
Highway Overpass
Ponce By-Pass
Ponce
B02R
PN10
12
Highway Bridge
Paso del Indio
Vega Baja
B03R
VGB1
24
Dam
Lucchetti
Yauco
D01M
YAC1
12
Dam
Carraizo
Trujillo Alto
D02M
TA02
9
Dam
La Plata
Toa Alta
D03M
TOA2
12
Table 1: Summary of Instrumented Structures Operated by PRSMP. Locations for
the sensors can be found in Figure 4.
27