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THE UNIVERSITY OF THE WEST INDIES ST. AUGUSTINE, TRINIDAD AND TOBAGO, WEST INDIES
THE SEISMIC RESEARCH CENTRE
Telephone: (868) 662-4659 E-mail: [email protected] Website: http://uwiseismic.com
Preliminary Earthquake Report
20180623 0154 UTC
Mt 5.5
STRONG MOTION PARAMETERS FOR PORT OF SPAIN FROM
LOCAL STRONG MOTION NETWORK
&
INTENSITY REPORT FROM
CITIZEN SEISMOLOGIST COMMUNITY PROJECT
Ilias Papadopoulos, Celeste Sobion & Hannah Ramsingh
Tel: 868-662-4659; Fax: 868-663-9293
Email: [email protected]
http://www.uwiseismic.com
2018/07/05
The results of the present report are preliminary and may be subject to revision if more detailed analyses will be
carried out.
The uncorrected data of the records in ASCII are available upon request.
DISCLAIMER
This report was compiled by the Engineering Seismologist of The University of the West Indies Seismic Research
Centre Ilias Papadopoulos. The accuracy and credibility of the results and the opinions expressed in this report are
solely his and do not necessary reflect those of the Centre.
Contents Summary ....................................................................................................................................................... 4
Earthquake Parameters (Source: UWI SRC) .................................................................................................. 5
Port of Spain General Hospital (PSGH) ....................................................................................................... 6
Strong Motion Parameters ........................................................................................................................ 7
Elastic Response Spectra (SA) .................................................................................................................. 8
Fourier Amplitude Spectra ........................................................................................................................ 9
PSGH Particle Motion ............................................................................................................................ 10
Comparison with IBC2000 Design Spectra ............................................................................................ 10
Kent House (PSKH) .................................................................................................................................... 11
Strong Motion Parameters ..................................................................................................................... 12
Elastic Response Spectra ......................................................................................................................... 13
Fourier Amplitude Spectra ...................................................................................................................... 14
PSKH Particle Motion .............................................................................................................................. 15
Comparison with IBC2000 Design Spectra .............................................................................................. 15
Mucurapo Girls RC (PSMG) ...................................................................................................................... 16
Strong Motion Parameters ..................................................................................................................... 17
Elastic Response Spectra (SA) ................................................................................................................. 18
Fourier Amplitude Spectra ...................................................................................................................... 19
PSMG Particle Motion ............................................................................................................................. 20
Comparison with IBC2000 Design Spectra .............................................................................................. 20
Woodbrook Secondary (PSWS).................................................................................................................. 21
Strong Motion Parameters ..................................................................................................................... 22
Elastic Response Spectra (SA) ................................................................................................................. 23
Fourier Amplitude Spectra ...................................................................................................................... 24
PSWS Particle Motion ............................................................................................................................. 25
Comparison with IBC2000 Design Spectra .............................................................................................. 25
Analysis of the Citizen Seismologist Community Project Felt Reports ....................................................... 28
Demographics ......................................................................................................................................... 28
Perception of Seismic Shaking Intensity ................................................................................................. 29
Summary
This document serves as a preliminary report for the moderate earthquake occurred in 2018/06/22, 01:54
UTC (21:54 local time) northwest of Trinidad (Coordinates 10.782N, 62.346W) (source:SRC). Its focal
depth of 107.52 Km allowed the shaking to be felt to a wider area. The Port of Spain Strong Motion Network
(POS SMN) recorded the event, and the strong motion data processing appears in this document. At the
second section of this document the intensity report is presented, as recorded by the SRC’s Citizen
Seismologist Community Project.
The maximum instrumentally recorded PGA value in the area of Port of Spain is recorded in Maraval, at
station PSKH (PGA= 0.510 m/s2), while the highest intensity values in Modified Mercalli Intensity (MMI)
Scale appear in reports from Maraval, Woodbrook and St. James (MMI=V). There have been no reports of
casualties or damages.
Initial results indicate that the western part of Port of Spain experienced higher seismic intensity compared
to the eastern side. This appears both in the instrumental recorded waveforms and community felt reports.
The geophysical survey conducted by SRC the past years in Port of Spain shows the western part to have a
thicker package of sediments compared to the eastern side, while the geological survey shows that the soil
deposits of the eastern side are more compacted. The areas of St. Claire, Woodbrook and St. James are the
natural flood plains of the Maraval River and the water table of the underground aquifer appears at
shallower depths at the west (less than 1m). All these indicate that the western side of Port of Spain is to
experience higher levels of shaking, especially as it gets closer to the coast, where also reclamation has
been conducted in the past.
Station PSWS, located at Woodbrook Secondary School, experienced a short break in transmission of data,
creating a gap in data recorded in the vertical component. We were unable to retrieve the whole waveform
for this component from that station, hence the results for this component are incomplete.
SECTION 1 STRONG MOTION PARAMETERS Earthquake Parameters (Source: UWI SRC)
Date 20180623
Time 0154 UTC
Latitude 10.782N
Longitude 62.346W
Depth 107.52 km
Magnitude (Mt) 5.5
Mean Epicentral Distance from POS SMN 92.5 Km
Mean Hypocetral Distance from POS SMN 140.5 Km
Mean Azimouth 98o
Figure 1. Google image showing the location of the earthquake event on June 6th, 2018 @01:54 UTC.
Port of Spain General Hospital (PSGH)
Port of Spain General Hospital (PSGH) Longitude W61.50807° Soil Type Soft
Latitude N10.66094° Vs30 (m/s) 420
Elevation (m) 15.5 NEHRP Class C
Building Structure Wood Resonance Frequency 2.2
Installation Surface/Concrete Sensor Guralp 5TDE
Telemetry Internet/Wired Digitizer Guralp DM24
Mean PGA (m/s2) 0.268 Mean Period (s) 0.18468
Figure 2. PSGH unfiltered waveform (Z: Vertical; N: North-South; E: East-West). Units in m/s2.
Strong Motion Parameters
Figure 3. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s2), V (cm/s), D (cm)
Elastic Response Spectra (SA)
Figure 4. Elastic Response Spectra. SA (top left), SV (bottom left), SD (top right) & all components @5% damping. Units: SA (m/s2), SV (cm/s),
SD (cm). Components: Z: Vertical; N: North-South; E: East-West.
Fourier Amplitude Spectra
Figure 5. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom).
Components: Z: Vertical; N: North-South; E: East-West.
.
PSGH Particle Motion
Figure 6. Particle motion, horizontal plane.
Comparison with IBC2000 Design Spectra
Figure 7. Comparison of elastic response spectra (SA) @5% damping with IBC2000 Design Spectrum.
Kent House (PSKH)
Kent House (PSKH) Longitude W61.52353° Soil Type Soft
Latitude N10.67958° Vs30 (m/s) 440
Elevation (m) 25.4 NEHRP Class C
Building Structure Free Field Resonance Frequency 3.2
Installation Surface/Concrete Sensor Guralp 5TDE
Telemetry Internet/Wired Digitizer Guralp DM24
Mean PGA (m/s2) 0.510 Mean Period (s) 0.24405
Figure 8. PSKH recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.
Strong Motion Parameters
Figure 9. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s2), V (cm/s), D (cm)
Elastic Response Spectra
Figure 10. Elastic Response Spectrum, Units: Units: SA (cm/s2), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.
Fourier Amplitude Spectra
Figure 11. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom).
Components: Z: Vertical; N: North-South; E: East-West.
.
PSKH Particle Motion
Figure 12. Particle motion, horizontal plane.
Comparison with IBC2000 Design Spectra
Figure 13. Comparison of elastic response spectra (SA) @5% damping with IBC2000 Design Spectrum.
Mucurapo Girls RC (PSMG)
Mucurapo Girls RC (PSMG) Longitude W61.53414° Soil Type Soft
Latitude N10.67219° Vs30 (m/s) 370
Elevation (m) 8.1 NEHRP Class C/D
Building Structure Free Field Resonance Frequency 1.4
Installation Surface/Concrete Sensor Guralp 5TDE
Telemetry Internet/Wireless Digitizer Guralp DM24
Mean PGA (m/s2) 0.315 Mean Period (s) 0.26992
Figure 14. PSMG recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.
Strong Motion Parameters
Figure 15. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s2), V (cm/s), D (cm)
Elastic Response Spectra (SA)
Figure 16. Elastic Response Spectra, Units: Units: SA (m/s2), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.
Fourier Amplitude Spectra
Figure 17. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom).
Components: Z: Vertical; N: North-South; E: East-West.
.
PSMG Particle Motion
Figure 18. Particle motion, horizontal plane.
Comparison with IBC2000 Design Spectra
Figure 19. Comparison of elastic response spectra (SA) @5% damping with IBC2000 Design Spectrum.
Woodbrook Secondary (PSWS)
Woodbrook Secondary (PSWS) Longitude W61.52061° Soil Type Soft
Latitude N10.66142° Vs30 (m/s) 363
Elevation (m) 5.5 NEHRP Class C/D
Building Structure Reinforced Concrete Resonance Frequency 0.9
Installation Surface/Concrete Sensor Guralp 5TDE
Telemetry Internet/Wireless Digitizer Guralp DM24
Mean PGA (m/s2) 0.276 Mean Period (s) 0.25189
Figure 20. PSWS recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.
Strong Motion Parameters
Figure 21. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s2), V (cm/s), D (cm)
Elastic Response Spectra (SA)
Figure 22. Elastic Response Spectra, Units: Units: SA (m/s2), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.
Fourier Amplitude Spectra
Figure 23. . Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio
(bottom). Components: Z: Vertical; N: North-South; E: East-West.
.
PSWS Particle Motion
Figure 24. Particle motion, horizontal plane.
Comparison with IBC2000 Design Spectra
Figure 25. Comparison of elastic response spectra (SA) @5% damping with IBC2000 Design Spectrum.
SECTION 2 MODIFIED MERCALLI INTENSITY REPORTS
Figure 26. Nationwide Modified Mercalli Intensity values.
Figure 27. Port of Spain Intensity map. With green dots the POS SMN is presented. Size according to
maximum recorded PGA value. Also shown is the MMI value from felt reports.
Analysis of the Citizen Seismologist Community Project Felt Reports
Demographics
Reports Demographics
Submitted 346 Urban Not available
Complete 346 Rural Not available
Reliable 342 Female 275
Usable 90 Male 65
Comments
Submitted: Total submitted online reports
Complete: Reports with all fields filled
Reliable: Reports considered filled with good will and faith
Usable: Reports with exact location to be place on a map
Urban: Total submitted reports indicating address in urban areas
Rural: Total submitted reports indicating address in rural areas
Female: Total submitted reports filled by female
Male: Total submitted reports filled by male
Perception of Seismic Shaking Intensity
From the statistical analysis of the reliable felt reports, the earthquake of 2018/06/23 @ 01:54 UTC was
reported felt in 97.2% of submitted reports. Most of the reports were filled by female (81%). The majority
of reports consider the earthquake shaking moderate (46%), while the shaking is described mostly as
trembling or swaying (32% and 33% respectively).
At the time of the event (21:54, local time) most people were awake and sitting still or laying down (88%).
The event caught T&T’s citizens by surprise (46%), while enough expressed fear (34%). Animals nearby
(indoors and outdoors) got upset (87%). Most submissions, report light swing of hanging objects (57%),
while doors, windows, china and glasses rattled (52-53%). The majority reports a sound effect (58%), which
appeared before (37%) or during (60%) the ground shaking. Reports are almost equally divided in the origin
of the sound effect, either from inside the building or from underground.
While no significant damages are reported, a small percentage of reports indicate cracks on the wall and
plaster falling from ceiling (6%). No other damage reported on walls or collapses.
The biggest concern from the authors of this report, is the amount of submissions that are unusable for
scientific research (74.4%), due to lack of precise location. While some citizens failed to provide an
address, by negligence or typing something irrelevant (e.g. my house) or providing fewer details (e.g.
Eastern Main Road), some others don’t have an address to report that can be of use (e.g. Lamp Post 23,
Maraval Road). Within the frame of Citizen Seismologist Community Project, an effort needs to be made
for these citizens to be able to determine accurately their location, in order for SRC to use the essential
information provided.