Automatic information and management system for the tsunami warning center Andreev A., Borodin R., Kamaev D., Chubarov L., Gusiakov V
Introduction The present work is focused on the developed methods, structure and principles of the automatic information-management system - a computer system for decision making support in tsunami-related emergency. This system has been developed and implemented as part of the Federal Targeted Program “Risk reduction and mitigation of consequences of natural and technology-related emergencies in the Russian Federation to 2010”.
Flow chart for computerized tsunami decision making Seismic event message Computer processing of seismic event message Identifying seismic event zones (near/far) Expected wave height calculations Computation of expected wave arrival time for threatened area, sea level measuring posts and visual observation posts Computerized decision making support to issue tsunami alert based on the magnitude-geographic criterion (message generation and dissemination) Computerized decision making support to tsunami alert cancellation based on refined wave heights in threatened areas and sea level visual observations Computer processing of data from measuring posts and visual observations of sea level: determination of actual arrival times and wave heights in threatened areas Data from sea level measuring posts Data of visual sea level observations
The decision making support system functionality • Presentation and monitoring of incoming messages and real-time data • Automatic selection of notification protocol based on submarine earthquake data • Implementation of logically related steps of event processing by duty oceanographer protocol in real time • Calculations of tsunami wave heights and arrival times for threatened areas, presentation and monitoring of calculations • Continuous analysis of sea level data coming from automated posts and calculations to detect tsunami wave emergence and estimate its key parameters: first wave arrival time, amplitude and period • Formation and automatic transmission of all output signals and messages by the notification protocol • Forecasting tsunami impact on coastal areas based on submarine earthquake data • Map-based presentation of spatially distributed data • Automatic documentation of all steps of event data processing
Computerized system for decision making support in case of tsunami threat The computerized system for decision making support in case of tsunami threat consists of: • integrated database • computation modules for estimating tsunami wave travel time and height • duty oceanographer workstation • control subsystem • telecommunication subsystem. • archived data viewer
Flow chart for operations of the computerized system of tsunami decision making support Seismic station Foreign TWCs Roshydromet automatic data transmission system Telegram distribution service Forming an earthquake signal Telegram sorting service Seismic event signal Task manager Incoming messages Calculation modules Signal and message monitor Sea level data analysis service Integrated database Signal and message log Action protocol Outgoing messages Browsing sea level data Measuring posts Telegram distribution service Archived data browser Roshydromet automatic data transmission system
Window of the duty oceanographer application and window of messages presentation and editing
Wave calculations for threatened areas Map-based data presentation (tsunami travel wave isolines, black point is the earthquake epicenter )
Wave calculations for threatened areas • The currently used methods of real-time prediction of tsunami characteristics are based on premodeling. Basically, premodeling consists in doing part of tsunami characteristics calculations in advance (before an event occurs) and developing a database to be used for calculations in real-time operations. • The database includes a set of elementary models of earthquake sources matching seismotectonic features of the water areas. For each model earthquake source, the expected wave heights are calculated. Results of calculations are entered into the database. • When a message on a seismic event with data, time, geographic coordinates of the earthquake epicenter and magnitude is received, the expected wave heights are calculated by interpolation of expected wave source parameters using the available database.
Rapture model • L - rapture length • W - rapture width • D - rapture upper end depth • Ψ - rapture strick azimuth • δ - rapture pitch angle • λ - rapturedirection • D - rapturevalue
Earthquake model sources in the Kuril-Kamchatka zone amplitude 7.8 and 8.4 In calculations the Kuril-Kamchatka core seismic zone was approximated by a system of model sources, their generalization mechanisms taken from historic records of tsunamigenic earthquakes in this region.
Earthquake model sources in the Kuril-Kamchatka zone • The distribution of the model earthquake sources with the magnitude of 7.8 was taken as baseline. The tsunami records suggest that this magnitude is a threshold for exciting tsunami posing threat to the east coast of the Kuril and Kamchatka. • The rapture surface dimension for sources of this magnitude was taken to be 109 km ×38 km, the subduction being 2.74 m. It was assumed that the primary mechanism for these sources was low-angle fault by the main lithosphere interface of this zone , i.e. by the border between the shoved ocean crust and the obducting edge of the continental lithosphere. It was assumed that the primary mechanism for these sources was low-angle overthrust by the main lithosphere interface of this zone, i.e. By the border between the shoved ocean crust and the obducting edge of the continental lithosphere. The slope angles of the rapture surface were taken to be 150, the subduction direction 900, which represents a low-angle overthrust. • In addition to the main system of model sources, sources with the magnitude 8.4 are used as the maximum possible submarine earthquakes for the region under study. The examination of the regional seismic catalogues has shown that there were only two events throughout the observational period with the magnitude exceeding this value: the Kamchatka earthquakes in 1923 and 1952
Map of earthquake sources with the magnitude 7.8 in the Japanese and Sakhalin zones
The Japanese and Sakhalin zones The submarine earthquake sources in the eastern sea of Japan were approximated with the system of shoves by the rapture surfaces (+700, -700) occurring along the contact zone of the Pacific and Filipino plates with the advancing Asian plate. The rapture surface areas for these earthquakes were taken to be the same as for the main system of sources located along the undersea trough. A chain of the sources stretches along the west coast of Japan from the Tsushima strait in the south to the vicinity of Kholmsk on the south-west coast, where the contact interface goes from the sea inwards the peninsula. In addition to this main system, a chain of sources between Sakhalin and Hokkaido was considered, where submarine earthquakes leading to insignificant tsunami in the south of Sakhalin occurred twice in the past ( in 1956 and twice in 1969).
Precalculation of tides For precalculations the following equation is used: (t)are the tidal variations in the sea level; fj is the reduction multiplier; Hj is the harmonic amplitude; t is the time; (V0 + u) is the astronomic argument; Gj is the position angle; j is the tidal harmonic frequency defined byhere mk = 0, = ±1, ±2, …; 0= 2/day, 2/k fj and (v0 + u)j are the function of time only and identical at a given time moment for any point on the Earth. The parameters fj and uj are changing slowly (the period 18.6 years), their variations over several months can be neglected. The value v0jis calculated as v0j = 0j + j(t - t0), where 0j is the phase at time moment t0, t represents the beginning of observations. Normally, 1 January 1900 is taken as t0. The values fj, v0and uj are calculated theoretically for any time moment, Hj, and Gj (the tidal harmonic constants) practically do not depend on time and are different for each point at sea. After determining once the harmonic constants with required accuracy, they can be used for precalculations of tides at a given point at any time.
Discrimination and identification of tsunami waves • In the first stage the tidal component is subtracted from the time series. Then, the sea level values after deduction of the tidal component are further processed . • In the second step, tsunami wave is discriminated against the natural noise. For this purpose, a special filter is applied to the observational series designed in such a way that its output signal is closest to the white noise characteristics where j is the output of the whitening filter, aj are the filter characteristics. The tsunami arrival time is determined by the excess above a specified value (threshold). Adjustment of filter parameters is done by the background non-tidal oscillations in sea level associated with meteorological impact on the sea (storm surge, seiche, surf beating). These oscillations are much smaller than tidal ones. The discrimination procedure is based on determining the rate of sea level change (with deduction of tidal component ) and its comparison with the characteristic rate occurring in the absence of tsunami (background oscillations in the sea level) . A significant excess in this rate is indicative of a tsunami signal. The rate of sea level change normally does not exceed 1-3 cm/min. For waves of hazard this value is as high as 10 or more cm/min.
Discrimination and identification of tsunami waves Window with results of processing sea level data and tidal calculations
Conclusion The nature of decision making on tsunami alert issue or cancellation does not let the process to be made completely automated: in some cases a decision is taken by a duty oceanographer on informal basis. The developed computer system provides informational and organizational support to decision making by a duty oceanographer in terms of: • real-time presentation of all available information on geophysical and seismologic situation • automation of message receipt and dissemination • automation of calculations to be done • prescribing actions of a duty oceanographer depending on the emerging situation • automatic recording of duty oceanographer actions, incoming and outgoing messages
Calculating tsunami wave travel times • M1contains nodes for which the travel time has been determined; • M2contains nodes for which the travel time had been determined beforehand; • M3contains nodes for which the travel time is not determined yet. the n-th step of the algorithmtakes nodes belonging to the set M2 in an ascending order: the working with nodes of the Influence domain: There are three possible cases: • , then the travel time of the node: , where is a distance along a larger circle arc between the nodes and is the depth at the node is the local wave propagation speed • , then the travel time need to be determined more precisely: After we have looked through all nodes in the influence domain the original point moved from the set M2 to M1. The described procedure is repeated for another node from the set M2 and on until the set M2 exhausted.
References • Federal law of 21.12.94 No 68-FZ “On protection of the population from natural and man-made emergencies ”(“Collection of laws of the Russian Federation), 1994, No 35, p 3648 ) • Regulation on the unified state system of emergency warning and management, as endorsed by the Government of the Russian Federation on 30 December 2003, No 794 (revision of the decree of the Government of the Russian Federation ) • Regulation on the operational tsunami warning subsystem of the unified state system of emergency warning and management (order No 171 of the Federal Service for Hydrometeorology and Environmental Monitoring of 01.08.2006) • Shokin Yu.I., Chubarov L.B., Marchuk An.G., Simonov K.V. Computational experiment on tsunami .- Novosibirsk, Nauka, Siberian division, 1989 -168 p • Report on project 4.2 of the state program “Safety”: “Development of scientific and methodological framework for organization and technology for conducting rescue and other emergency activity in case of disastrous inundation” – M, Research institute of civil defense and emergencies, 1995, 255 p • Common interagency methodology for estimating damage from technology-related, natural and terrorist emergencies and classification and recording of emergencies – M, Ministry of emergencies, Russia,2001 • Gusanov A.Z., Ryzhov I.V., Chebtarev S.S. Economic implications of emergencies and methodologies to estimate social and economic damage. Teaching aid. Academy of civil defense, Novogorsk - 1999 • Guidance on tidal data processing and tide prediction. L., Publisher: USSR Navy Hydrography, Leningrad, 1941, 347 p