State and perspectives of
development for the sakhalin operative tsunami warning service
Tatiana N. Ivelskaya,
Director of Sakhalin Tsunami Warning Center
Tsunami Warning Service (TWS) in Russia was established after disastrous tsunami in November 4th, 1952. The service is under the jurisdiction of two ministries. Federal Service of Hydrometeorology and Russian Academy of Sciences. Sakhalin Tsunami Warning Center together with Seismic Station "Yuzhno-Sakhalinsk" fulfil a operative warning services of a tsunami dangerous for Sakhalin isl., Primorie coastal in the Japan sea and for Kurily islands. The seismic station is responsible of alarm proclaim for a near earthquakes alarm proclaim, with epicentral distance to 3000 kilometers from Yuzhno-Sakhalinsk. Tsunami Warning Center is responsible for all another cases, and also for alarm of strong earthquakes in the Pacific Ocean with the epicentral distance more than 3000 km.
The basic method to acceptance the operative decisions about tsunami alarm is a
forecast of possible a tsunami dangerous, by using a supervision at only one seismic
station. "Yuzhno-Sakhalinsk" seismic station is fulfil such part. In advance of
forecast for a coastal, in adverse cases, makes about 15-20 minutes. Earthquake is account
as a dangerous, if its epicenter coordinates find in a local epicentral zone, and
magnitude is more then 7. 0. For example, in the Kuril-Kamchatka epicentral zone is using
a critical magnitude is 7.0. Manual processing of analogue seismograms in our
"Yuzhno-Sakhalinsk" seismic station, for a earthquake with epicentral distance
of 1000 km, has not then 10 minutes, after beginning of strong earthquakes registration.
Nowadays has kept serviceability one local seismic station in the Severo-Kurilsk town,
that place on a Northern Kuril islands, which fulfil supervision and responsible for
acceptance of decisions on a tsunami alarm in the local area.
On a coastal hydrometeostations, after reception a signal of tsunami dangerous
possibility, secondary one may be command from TWC about beginning continuous supervision
for all sea elevation variations. Data about sea level condition, and also beginning and
all characteristics of sea floods or tsunami, by urgently communication sending to TWC for
analyses and acceptance of following decisions. Really it is a telex (telegraph)
communication from a small town, and short-wave radio channels from taiga posts. In a
important part of this message there is a case to tell about of our considered projects
and of future technical organizational plans.
It is proposals was account the current services situation:
1) After receiving data of location and magnitude of strong seaquake, the TWC makes fast calculations for tsunami fronts propagation, and for tidal sea elevation mode for all of warned states and for protected coastal regions. This results insert to warning messages lists and immediately deliveries to 10-15 address, by using telegraph and telex line. For messaging there are three messaging scheme: 1-Kuril isls.; 2-Primoriue and Sakhalin's Tatar strait shore; 3-Okhotsk sea coastal. For a near earthquake, the Sakhalin TWC make a messaging to 6-10 minutes after receiving a warning from seismic subsystems of Tsunami Services.
New software nowadays accustoms, which allows not only to expect times of tsunami waves approaching to coast, but also to estimate amplitudes of sea elevation at the first moment of a tsunami front contact with a coastal points.
The second evaluation stage for estimates of a tsunami dangerous on a shore will begin after getting the operative data from the coastal posts of supervision about amplitude and period of an observable wave near from the shore. It is enough for the approached estimation of the maximal amplitudes of a tsunami, and long time of their occurring and the possible continuance of dangerous situation. Which using a preliminary solves computed long wave oscillation characteristics of a shelf zone near to particular places on the shore. For this purpose will be using a special electronic databases, founded on a results of the computational experiments and natural supervisions near to coast are used. In the computers realization it is a nomograms for a transfer functions and speeds of decreasing for each possible tsunami fronts directions and waves periods, for all possible posts of tsunami wave observations.
The modern personal computer (PC) facilities quite successfully allow to realization of directly numerical simulations of the tsunami waves propagation and dynamics. Which simulations must be started immediately after receiving of seaquake characteristics, and continuously computing on one of computers in a background mode, during all services action of distributing situation. Such simulations are necessary for visual representation of ocean hydrodynamic processes and long wave dynamics near to coastal. It is necessary for acceptance of the reasonable decisions for activation or stops of actions on an alarm, also for consulting of safety divisions at origin of catastrophic consequences.
The first attempt of modeling a tsunami was made directly in Sakhalin center a tsunami on October 5, 1994. Computing resources of the computer PC-386/25), according to approximation criterion, allowed to carry a wave on Yuzhno-Kurilsk strait with period no less than 12 minutes. The settlement area got out proceeding of speed of calculations on given PC, and the size it was such, that the source of earthquake appeared outside of this area. Then as a source a single wave with period 12 minutes, come in Yuzhno-Kurilsk strait from southeast was chosen.
By results of accounts character of distribution of amplitudes the tsunami on Southern Kuril islands was determined, where factor of strengthening of amplitude a tsunami was operatively correct under the message from ship radiostation about a tsunami in Malokurilsk bay, equal to 2 meters. On the basis of computing experiment, group structure of wave packages is determined which were displayed maximum run-ups on coast of islands Yuzhno-Kurilsk strait with periodicity approximately equal to 2 hours. The alarm a tsunami was cancelled at 8 o'clock 45 minutes of Sakhalin time, and by results of accounts the last large wave a tsunami passed about Yuzhno-Kurilsk at 9 o'clock in the morning on October 5, that was marked during operative negotiations with the observers in Yuzhno-Kurilsk.
In subsequent, in accordance with accumulation of materials about earthquake and the tsunami on Southern Kuril islands, was made a new series of computing experiments, with use more powerful PC: IBM- PC 486/66. First of all account return isochronal from Kushiro, Hanasaki, Malokurilsk and Youzno-Kurilsk was made which from two parties concern to the source a tsunami.
By results of specified modeling a tsunami with the help of the executor task of the center, and after comparison with results expedition of measuring and records tidal gauge, the operative numerical modeling on October 5, 1994 is possible consider quite satisfactory and extremely useful for use in an operative service of the warning about a tsunami and, especially, for an estimation of influence a tsunami on coast, during realization warning. The revealed lacks on fall of amplitude on borders of settlement area can be easily eliminated by increase of computing capacity PC, that was shown by the subsequent modeling on the specified centers. The discrepancies in determination of a source of earthquake are very quickly eliminated under the messages on passage of a real tsunami on coast. The specified specifications are quite allowable, as at realization of computing experiment on the basis of model of long waves, the simulated process operates just with factors of strengthening.
The greatest efficiency of aforesaid limited actions can bring in future, in a case of installation of the automated systems for the observations a sea fluiddynamics condition, bringing operative data to the TWC by telemetering communication channels. Such operative systems will allow to automate and essentially increase accuracy of results both at performance of expert estimations, and at realization of directly computational experiments. But the important, the automated observation will supply the warning not only about a tsunami, also other dangerous sea floods, which regularly bring damage to a national economy of Sakhalin region.
At means regional budget, in the Computational Fluid Mechanics & Oceanography laboratory (dr. Khramushin) begun a project for adaptations new computational experiments for really tsunami propagation and also for automation for warning telexes messaging.
Nowadays we have a project, which is under consideration in the Sakhalin Region Administration. According to this project must be established two automatic devices with a telemetric data communication for continuously observation of a coastal sea elevations. One in South-Kurils for warning and safety island's coastal, which very often attacked by sea floods, and the second device for the Korsakov city, where this device will be accessed for all-the-year-round maintenance, modification or for another scientific experiments.
Also, tsunami researches are supported by Russian Foundation for Basic Researches N 97.01.96010 and new internet communication with supported by Eurasia Foundation grant V97-0696.
Tatiana. Ivelskaya,
Director of Sakhalin Tsunami Warning Center
TWC@Sakhalin.ru