Abstract

In the area 30-33°S, 116-118°E of the Southwest Seismic Zone of Western Australia, ML -4.0 earthquakes for the period 1960-1983 do not fit a Poisson model. However, when foreshocks and aftershocks are excluded, the hypothesis of a Poisson distribution cannot be rejected for the resulting series of main shocks. A similar result holds for the subset of ML -5.0 events for the period 1949- 1983. Consequently, when earthquake risk is being assessed by methods that assume a Poisson distribution, foreshocks and aftershocks should be excluded . However, the consequent apparent reduction of risk caused by removing these potentially damaging earthquakes should be pointed out. Although records of seismicity are probably incomplete for the early part of this century, there appears to have been an increase in numbers of ML -4.0 events, starting around 1949. Although, the data are too uncertain to test the increase in the ML -4.0 main shocks statistically, there has been an approximate five-fold increase in the mean yearly number of ML -4.5 main shocks during the period 1949 to 1983, compared with the period 1923 to 1948. This is clearly larger than would be expected from a Poisson process. Consequently, the apparent increase in the number of ML -4.0 events is probably also real and not an artefact of a Poisson process. Also, there were no ML -5.0 events during the period 1923 to 1948, and the only two ML -6.0 earthquakes this century took place in 1968 and 1979. This increase in seismicity since the late 1940s should be taken into account in the interpretation of earthquake risk calculations.
Google map showing geographic bounding box with values North bound -27.6 East bound 120.37 West bound 115.1 South bound -33.55
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Product Type/Sub Type

nonGeographicDataset

Constraints

Creative Commons Attribution 4.0 International Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

1987-01-01T00:00:00

Product Type

nonGeographicDataset

Topic Category

geoscientificInformation

GA Catalogue Number

81211 Product http://www.ga.gov.au/metadata-gateway/metadata/record/81211/

Keywords

GA Publication
Journal
WA
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-27.6
East bound
120.37
West bound
115.1
South bound
-33.55

Lineage

Unknown

Digital Transfer Options

onLine

Distributor

Role
distributor
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Source Description

Source data not available.

Metadata File Identifier

fae9173a-7098-71e4-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

Role
pointOfContact
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
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