Preliminary Earthquake Reportuwiseismic.com/Downloads/20180522_Strong_Motion_Report.pdfKent House (PSKH) Kent House (PSKH) Longitude W61.52353 Soil Type Soft Latitude N10.67958 Vs

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

mailto:[email protected]

http://uwiseismic.com/

mailto:[email protected]

http://www.uwiseismic.com/

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


Elastic Response Spectra (SA) ................................................................................................................. 18


PSMG Particle Motion ............................................................................................................................. 20


Woodbrook Secondary (PSWS).................................................................................................................. 21


Elastic Response Spectra (SA) ................................................................................................................. 23


PSWS Particle Motion ............................................................................................................................. 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


Telemetry Internet/Wired Digitizer Guralp DM24


Figure 8. PSKH recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.



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.




.

PSKH Particle Motion




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


Telemetry Internet/Wireless Digitizer Guralp DM24


Figure 14. PSMG recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.




Figure 16. Elastic Response Spectra, Units: Units: SA (m/s2), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.




.

PSMG Particle Motion




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


Telemetry Internet/Wireless Digitizer Guralp DM24


Figure 20. PSWS recording (Z: Vertical; N: North-South; E: East-West). Units in m/s2.




Figure 22. Elastic Response Spectra, Units: Units: SA (m/s2), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.


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




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.

Documents

Preliminary Earthquake Reportuwiseismic.com/Downloads/20180522_Strong_Motion_Report.pdfKent House (PSKH) Kent House (PSKH) Longitude W61.52353 Soil Type Soft Latitude N10.67958 Vs