Journal of Ocean and Climate: Science,Technology and Impacts

The Cook Strait Canyon is a submarine canyon which lies within 10 km of Wellington, the capital city of New Zealand. The canyon flanks are scarred with the evidence of past landslides that may have caused large local tsunamis. City planning and civil defence management require information on the magnitude and frequency of these tsunamis to adequately plan for them. Submarine-landslide-generated tsunamis are by nature local features. While they may be catastrophic in the near field, they are generally far smaller scales than co-seismic tsunamis and their energy does not travel very far. Including them within a comprehensive tsunami hazard assessment requires accounting for a large number of potential landslide sources. Unless we only use simple rules of thumb to approximate tsunami height, this requires considerable computing power. This article describes a technique for expanding two-dimensional vertical-slice tsunami generation by landslide modelling into a two-dimensional horizontal surface which can be used for tsunami propagation and inundation modelling. As such, it spans the gap between full three-dimensional modelling of the landslide and simple initialisation.

Natural processes like wave action, tides, winds, storm surges, and tsunamis constantly shape the shoreline by inducing erosion and accretion. Coastlines with intact vegetated dunes, mangroves, and reefs act as a buffer zone against wave attack on beaches. This article discusses the effect of simulated seagrass on wave height attenuation and wave run-up through an experimental study. The tests were carried out with submerged artificial seagrass subjected to varying wave climate in a 50-m-long wave flume. Measurements of wave heights along the seagrass meadow and the wave run-up on a 1:12 sloped beach were taken for wave heights ranging from 0.08 to 0.16 m at an interval of 0.02 m and wave periods 1.8 and 2 seconds in water depths of 0.40 and 0.45 m.

The Indian Tsunami Early Warning System situated at Indian National Center for Ocean Information Services, Hyderabad, India, monitors real-time earthquake activity throughout the Indian Ocean to evaluate potential tsunamigenic earthquakes. The functions of the Indian Tsunami Early Warning System earthquake monitoring system include detection, location and determination of the magnitude of potentially tsunamigenic earthquakes occurring in the Indian Ocean. The real-time seismic monitoring network comprises 17 broadband Indian seismic stations transmitting real-time earthquake data through VSAT communication to the central receiving stations located at the Indian Meteorological Department, New Delhi, and the Indian National Center for Ocean Information Services, Hyderabad, simultaneously for processing and interpretation. In addition to this, earthquake data from around 300 global seismic stations are also received at the Indian National Center for Ocean Information Services in near-real-time. Most of these data are provided by IRIS Global Seismographic Network and GEOFON Extended Virtual Network through Internet. The Indian National Center for Ocean Information Services uses SeisComP3 software for auto-location of earthquake parameters (location, magnitude, focal depth and origin time). All earthquakes of Mw >5.0 are auto-located within 5–10 minutes of the occurrence of the earthquake. Since its inception in October 2007 to date, the warning centre has monitored and reported 55 tsunamigenic earthquakes (under-sea and near coast earthquakes of magnitude ⩾6.5) in the Indian Ocean region. Comparison of the earthquake parameters (elapsed time, magnitude, focal depth and location) estimated by the Indian Tsunami Early Warning System with the US Geological Survey suggests that the Indian Tsunami Early Warning System is performing well and has achieved the target set up by the Intergovernmental Oceanographic Commission.

A systematic study of geophysical data of the Eastern Continental Margin of India was taken up to identify the land–ocean tectonic lineaments over the east coast of India and the possible neotectonic activity associated with them. These studies helped in delineating the offshore extension of some of the coastal lineaments. Analysis of magnetic, gravity and shallow seismic data, combined with reported seismicity data, indicates moderate seismicity associated with some of these land–ocean tectonics of the Eastern Continental Margin of India. The coastal/offshore regions of Vizianagaram (north of Visakhapatnam) and Ongole of the Andhra Pradesh margin and the Puducherry shelf of the Tamil Nadu margin have been identified as zones of weakness where neotectonic activity has been established. Bathymetry data over the Eastern Continental Margin of India revealed the morphology of the shelf and slope of this margin, which in turn can be used as the baseline data for tsunami surge models. Detailed bathymetry map and sections of the Nagapattinam–Cuddalore shelf (from 10.5° to about 12°N) indicate that one of the main reasons for the higher run-up heights and inundation in the Nagapattinam–Cuddalore coast during the Indian Ocean Tsunami of 26 December 2004 could be the concave shape of the shelf with a gentle slope, which might have accelerated the tsunami surge to flush through at a rapid force. Structural control also appears to be a contributing factor for the tsunami surge.