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Haiti earthquake shaking amplified by local landforms

Haiti earthquake shaking amplified by local landforms

PORT-AU-PRINCE, Haiti — The severe damage and loss-of-life caused by the devastating January 2010 M7.0 earthquake in Haiti was exacerbated by amplification of shaking due to local geological conditions and landforms in Port-au-Prince, according to a study published online today in Nature Geoscience.

Following the earthquake, Susan Hough, a U.S. Geological Survey geophysicist, led a team from the USGS and the Haitian Bureau des Mines et de l’Energie that deployed a total of nine portable seismometers in Port-au-Prince to investigate the variability of shaking throughout the city. The aftershock recordings captured by the seismometers revealed that ground motions were amplified by the relatively young and soft rocks that underlie the valley in which the city is situated. The strongest observed amplifications were along a narrow, steep foothill ridge in the district of Petionville.

Shaking in any earthquake can be amplified significantly by local geological conditions.  Amplification due to topographic features, such as ridges, has been considered less important than amplification due to near-surface geological structure.

In Haiti, the zone where high shaking amplification was observed corresponded with a swath of high damage during the January mainshock.  A number of substantial structures in this region collapsed catastrophically, including several United Nations Development Programme offices and several large hotels. 

The instrument deployment was undertaken as a partnership effort between the USGS and the Bureau des Mines et de l’Energie, which continue to work together to establish a permanent seismic monitoring network in Haiti.

The study underscores the need to consider seismic provisions in the rebuilding effort, and suggests that topographic effects should be considered when detailed hazard zone maps are made for other regions.

USGS Newsroom

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Parameter Value Description
Magnitude mb The magnitude for the event.
Longitude ° East Decimal degrees longitude. Negative values for western longitudes.
Latitude ° North Decimal degrees latitude. Negative values for southern latitudes.
Depth km Depth of the event in kilometers.
Place Textual description of named geographic region near to the event. This may be a city name, or a Flinn-Engdahl Region name.
Time 1970-01-01 00:00:00 Time when the event occurred. UTC/GMT
Updated 1970-01-01 00:00:00 Time when the event was most recently updated. UTC/GMT
Timezone offset Timezone offset from UTC in minutes at the event epicenter.
Felt The total number of felt reports
CDI The maximum reported intensity for the event.
MMI The maximum estimated instrumental intensity for the event.
Alert Level The alert level from the PAGER earthquake impact scale. Green, Yellow, Orange or Red.
Review Status Indicates whether the event has been reviewed by a human.
Tsunami This flag is set to "1" for large events in oceanic regions and "0" otherwise. The existence or value of this flag does not indicate if a tsunami actually did or will exist.
SIG A number describing how significant the event is. Larger numbers indicate a more significant event.
Network The ID of a data contributor. Identifies the network considered to be the preferred source of information for this event.
Sources A comma-separated list of network contributors.
Number of Stations Used The total number of Number of seismic stations which reported P- and S-arrival times for this earthquake.
Horizontal Distance Horizontal distance from the epicenter to the nearest station (in degrees).
Root Mean Square sec The root-mean-square (RMS) travel time residual, in sec, using all weights.
Azimuthal Gap The largest azimuthal gap between azimuthally adjacent stations (in degrees).
Magnitude Type The method or algorithm used to calculate the preferred magnitude for the event.
Event Type Type of seismic event.
Event ID Id of event.
Event Code An identifying code assigned by, and unique from, the corresponding source for the event.
Event IDS A comma-separated list of event ids that are associated to an event.

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