Earthquakes are ever-present in PNG. They happen anytime and without warning. They present a constant threat to communities and infrastructure. PNG region is categorised as one of the most seismically active parts of the world. Large damaging earthquakes (M ≥ 7) have been recorded and in many cases have resulted in loss of lives and damage to property, both personal and public.
Monitoring of earthquakes in the PNG region is done using a network of seismic stations, strategically-located country-wide. Earthquakes of varying sizes are recorded by the stations of this seismic network. Locally-induced earthquakes as well as regional and distant events are also recorded.
Distribution of earthquakes in PNG
The distribution of earthquakes provides a general guide to the level of seismicity of a region. Earthquake database containing information about earthquakes that occurred in the PNG region since 1900 is maintained by PMGO. Using appropriate computer software, staff at PMGO determines the location and magnitude of the earthquakes. Results of these analyses are routinely checked against the results determined by other agencies, and re-determinations are made where necessary to reduce location uncertainties. From these data, areas of seismicity are defined and progressively being refined as more seismic data becomes available.
Dissemination of earthquake information and alerts
For significant earthquakes (M ≥ 6), they are analysed and details made known promptly to the disaster authorities, relevant Government agencies, mainstream media and the general public, via a range of communication channels. A follow up information is disseminated if required. Questionnaires are sent to the regions that felt the event for descriptive assessment of the effects of the earthquake.
Earthquake warning and response
Issuing of warning for an earthquake event is not possible due to the unpredictable nature of earthquake triggering processes inside the earth. Since earthquakes occur without warning, emphasis has been placed on educational awareness and preparedness as a mitigation tool for effective response.
For precautionary measures, whenever a severe earthquake occurs, the most effective way to protect oneself from harm during the earthquake shaking is to Drop, Cover, and Hold On, until the shaking eases.
Large magnitude earthquakes
Since earthquake observations began in PNG in the mid 1950s, large magnitude earthquakes (M ≥ 7) have been recorded across PNG. Prior to that, pre-colonial administrations have also documented large earthquakes from reports and assessments of earthquake effects on people and properties. Many have generated secondary effects such as triggering notable landslides and tsunamis. Few of the recent notable earthquakes include:
- 26th February 2018, M7.5, Tari earthquake.
- 16th November 2000, M8.0, New Ireland earthquake.
- 08th February 1987, M7.4, Umboi Island earthquake
- 31st October 1970, M7.0, Adelbert Range, Madang earthquake
Seismic hazard assessment
The actual ground shaking is the hazard triggered by an earthquake. Severe ground shaking increases the hazard. Earthquake ground shaking can significantly affect engineering structures such as buildings, bridges, dams and roads, built on the surface of the ground. Some of these buildings house critical facilities such as banking systems, communication facilities, hospitals, schools, etc., that supports livelihood.
Seismic hazard assessment in the PNG region has been done in a series of recent studies. On a national, regional scale, studies have been conducted to determine return periods and probabilities of occurrence of large earthquakes. These studies have contributed to the definition of seismic zones in PNG and the establishment of the PNG Building Code. The results of this work are routinely applied to areas of specific concern such as population centres for public safety considerations and also in the vicinity of industrial (including mining and petroleum) development projects.
Earthquake source zones
Delineation of earthquake source zones from a range of research undertaken has enlightened the knowledge of tectonic micro-plate boundaries within the PNG region. On-going seismological studies are refining the tectonic structure and dynamics of the PNG region on both large and smaller scales. The boundaries of the lithospheric plates are becoming clearer, although some boundaries remain uncertain. As more data becomes available, it increases the level of understanding of the seismo-tectonic processes and the geodynamics of the region.
On a smaller scale, a number of recent studies have shown the value of monitoring earthquake sequences (main event and aftershocks) which have resulted in mapping of active faults and determination of sense of motion on the faults. The progressive study of earthquake sequences helps to define crustal structure both by direct evidence on individual faults and by association between elements of fault systems.