Two estimates of economic benefits have been derived for Hawaii. A second estimate is based on nearly identical earthquakes off the Aleutian Islands before and after the existence of the DART network. On November 17, , a DART station offshore of the Aleutian Islands clearly showed that a sizable tsunami was not generated by a magnitude 7.
These findings are consistent with cost estimates associated for unnecessary hurricane evacuations along the U. Clearly, unwarranted evacuations can cost millions of dollars; and, although the costs associated with the loss in public confidence are less easy to quantify, the effectiveness of a warning system is ultimately grounded in credibility. Although the DART stations have their greatest value in discerning tsunami propagation characteristics in the open ocean, the inundation problem requires, ideally, sea level sensors along tsunami-prone coastlines because of the spatial variations in tsunami height that are produced by local bathymetry, coastal geometry, and the resultant system responses e.
Although coastal sea level stations were originally installed for monitoring tides for navigational purposes, most now serve a broad range of uses including tsunami detection that have contributed to their continued support and upgrades. Stations are commonly located deep within harbors or bays, where nonlinear hydrodynamic effects and local geographic complexity strongly alter the structure and amplitude of any impinging tsunami waveform. These non-. Tide stations were typically configured to measure sea level height in a stilling well, a vertical pipe that is secured to a piling, pier, wharf, or other shore-side structure.
These pipes have a small orifice s to allow water to enter relatively slowly thus filtering out the short period seconds wind waves, and even tsunamis, so that the hourly recorded sea level values from within the pipe are not aliased by the short period variability.
This technology works well for measuring tides and other long period phenomena, but even if the sampling rate is increased from hourly to minutes the true tsunami signal may not be well observed given these filtering effects. Furthermore, a large tsunami can overtop a well and render it useless in extreme events. Consequently, sea level observations intended for tsunami detection are now often accomplished inside a tsunami-hardened station equipped with a rapid-sampling pressure, acoustic, or microwave sensor with an orifice set apart from the structure National Tsunami Hazard Mitigation Program, The most important roles for coastal sea level data in the tsunami forecasting and warning process are currently the initial detection of a tsunami, scaling the tsunami forecast models in near-real time, and post-tsunami validation of tsunami models see Weinstein, ; Whitemore et al.
These roles require accurate, rapidly sampled sea level observations delivered in near-real time via an appropriate telemetry system. In practice, these requirements translate into a need for sea level averages at least as often as every minute that are made available in near-real time U.
Indian Ocean Tsunami Warning System Program, , and a need for assiduous maintenance of the sea level gauges so that near-real-time data can be trusted and will be available most of the time. Furthermore, subsequent to collection, the data need to be carefully processed through a set of rigorous quality control procedures to maximize the value for model validation after the fact U.
As an example of the importance of high temporal data resolution, Figure 4. Indian Ocean Tsunami Warning System Program, for sea level stations that are intended to provide data for tsunami warning. For coastal tide gauge stations, the requirements are:. One-minute samples are shown in red; two different gauges providing 6-minute samples are shown in green and orange.
Note that the 6-minute samples completely miss the highest amplitude component the third crest and trough of the tsunami. Note the minor beam aimed at Crescent City, California, where the boat harbor was damaged, largely by secondary tsunami waves. However, following the devastating Indian Ocean tsunami, and with the support authorized in P. The increased data sampling and transmission rates advance the objectives of tsunami detection and warning, as well as to provide critical inundation model input. West Coast, and the Caribbean, increasing the geographic coverage of water level observations in tsunami-vulnerable locations.
Color codes indicate the authorities responsible for gauge maintenance. The positions of the original six DART buoys yellow triangles existing in before the enactment of P. Upgraded tide stations are equipped with new hardware and software to enable the collection and dissemination of 1-minute water level sample data.
This webpage allows users to view both 6- and 1-minute data numerically or graphically for all tsunami-capable tide stations in increments of up to 4 days Figure 4. Like the near-real-time data, all water level data displayed through the CO-OPS tsunami webpage are raw and unverified at this time. The second data, potentially more useful for model validation, are not telemetered on a regular basis, but are available to the TWCs via remote phone dial-in.
Indian Ocean Tsunami Warning System Program, the performance and maintenance standards it recommends for sea level stations that are intended to aid tsunami detection, forecasting, and warning activities. Whether sea level gauges operated and maintained by other U.
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In addition, the committee is not aware of any process by which the non-NOS sea level stations U. The mission of the UHSLC is to collect, process, distribute, and analyze in-situ sea level gauge data from around the world in support of climate research. The TWCs operate a small subset of coastal tide stations Figure 4. In general, the TWC stations are not maintained to the specifications of the NWLON but have historical precedence and fill gaps in the observing array or fill specific local needs.
For example, the PTWC gauges on the Big Island of Hawaii will provide about 20 minutes of warning for Honolulu should a large amplitude tsunami be generated by an earthquake or landslide on the Big Island. The TWCs have indicated they do not have the resources to properly maintain these gauges or to process, distribute, and archive the data. The website serves as a central clearinghouse of data from a range of international providers, including the data sources mentioned above.
The objectives of this service are to provide information about the operational status of global and regional networks of near-real-time sea level stations and to provide a display service for quick inspection of the raw data stream from individual stations. SLSMF is an appropriate place to obtain such reliability information because it lists only data that were initially made available in near-real time over the GTS, not what was eventually available after internal memory was finally accessed during a maintenance operation.
Indian Ocean Tsunami Warning System Program, performance and maintenance standards has not been determined. Following the disastrous Indian Ocean tsunami, many additional global sea level observing stations have become available for the purpose of tsunami detection and warning, including those enabled in the United States by P. Despite this increase in the number of near-real-time-reporting, rapid-sampling coastal sea level gauges, a map of the sea level station coverage e.
In addition, this dependence on data supplied by foreign agencies, although mitigated somewhat by the redundancies and overlaps in coverage, exposes a vulnerability of the tsunami detection and warning activities to potential losses in data availability. A recent earthquake in the Caribbean illustrates the issue of coverage.
On May 27, , a magnitude 7. Worst-case-scenario tsunami forecast models suggested tsunami amplitudes up to nearly 1 m given initial earthquake source parameters. No rapidly sampled, near-real-time sea level gauges exist in the western Caribbean, so the PTWC could only wait for visual reports. However, enough time has passed that any nearby areas should already have been impacted. Gaps in the coastal sea level network exist, such as revealed by the Honduran earthquake in May No analysis has been undertaken to evaluate critical coverage gaps with regards to the tsunami warning decision process.
Furthermore, no analysis has been undertaken to determine the relative importance of each existing coastal sea level gauge to the tsunami warning decision and evacuation decision processes. Although there is some degree of redundancy in coverage in the current sea level gauge network for some purposes, there has been no evaluation of the associated risk and the vulnerability of the warning process to failures of single or multiple stations. The spacing of sea level gauges for the purpose of tsunami detection is sparse, because it is now known that tsunamis can be quite directional, focusing the majority of their energy within a narrow sector, perpendicular to the seafloor rupture direction.
For instance, Figure 4. Given the array of sea level gauges in Figure 4. Had the Midway Island station been temporarily inoperative, forecasters. As it was, the Midway Island record confirmed that the tsunami was not going to significantly threaten lives or property in the main Hawaiian island, and no evacuation order was issued.
Although many gaps exist in the sea level network for rapid tsunami detection, limitations in U. A sophisticated analysis is needed to evaluate critical coverage gaps for coastal sea level gauges to inform the warning decision process. Such an analysis could also determine the relative importance of each existing coastal sea level gauge to the tsunami warning decision and evacuation decision processes. Although there is some degree of redundancy in coverage in the current sea level gauge network, there has been no evaluation of the associated risk and the vulnerability of the system to failures of single or multiple stations.
It is possible that isolated gauges near historically tsunami-producing seismic zones would be considered highly important, while individual gauges among a relatively compact group of gauges might be considered less important although the need for at least one gauge within the group might be considered highly important.
Such an assessment of the relative importance of existing gauges could then be the basis of prioritization for maintenance schedules and enhancement opportunities, and for the identification of critical stations that are not under U. In order to mitigate the cost of enhancing and maintaining tsunami-useful sea level monitoring stations, the U. Tsunami Program could continue coordinating with other programs interested in monitoring sea level variability for other purposes, such as climate variability.
Coastal stations with a broad user base have enhanced sustainability. International coastal sea level networks vary greatly in station density, transmission rates, and data quality. Improved near-real-time international sea level data observations are crucial to proper TWC response for events distant to U. Recommendation: Two important concerns regarding the entire coastal sea level network employed by the TWCs in their warning activities need to be addressed soon, as follows:. A priority list of the coastal sea level stations should be constructed, based at first on the experience of the TWC forecasters, and later updated from the results of the more objective coverage analysis described in the previous section.
A risk assessment of the data flow from the highest priority stations should be performed. As an example of prioritization, note that as of June 26, , all five DART stations covering the Aleutian Islands west of the Dateline, and the Kuril Islands to Hokkaido, had been inoperative for nearly all of Such failures meant that the Midway Island coastal station at Therefore, the Midway Island station is a strong candidate for high-priority status. SLSMF also has the information needed to determine data stream reliability, at least since SLSMF is actually a very appropriate place to obtain such reliability information because it lists only data that was initially made available in near-real time over the Global Telecommunications System, not what was eventually available after internal memory was finally accessed during a maintenance operation.
The data streams under consideration included, among others, sea level data from DART buoys and from U. The committee identified findings in NTHMP with respect to processing, distribution, archiving, and long-term access to tsunami-relevant sea level data that remain highly relevant today including the following issues:.
Chilean Earthquake Restores Beaches
There is currently no routine acquisition of the second CO-OPS data, which are most relevant for model validation, and there is no routine retention of these data. Fifteen-second data are only collected on request and have no quality control or archive. One-minute data are not currently quality controlled to the same level as the six-minute data. The absolute time accuracy of second data 30s Nyquist period should be 0.
Time accuracy at this level is required in order to preserve phase relationships at the highest observed frequencies i. Such absolute accuracy is not difficult to achieve. Address 1-minute and second quality control issues in unison with the archive issue to ensure quality of archive. Create an operational website providing a portal for second tsunami station water level data.
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This committee did not undertake an assessment of the processing, distribution, archiving, and long-term access to tsunami-relevant sea level data originating from international sea level stations. Conclusion: Despite the excellent accomplishments by NOAA with respect to improving the processing, distribution, archiving, and long-term access to the tsunami-relevant sea level data that it collects, there remain several inadequacies.
To ensure early detection of tsunamis, especially where the coastal sea level network is sparse or nonexistent, and to acquire data critical to near-real-time forecasts, NOAA has placed. DART stations in regions with a history of generating destructive tsunamis. A DART station comprises an autonomous, battery powered, bottom pressure recorder BPR on the seafloor and a companion moored surface buoy that forwards the data it receives acoustically from the BPR to an onshore receiver via satellite links Figure 4.
The BPR collects and internally stores pressure and temperature data at second intervals. The stored pressure values are corrected for small temperature-related offsets and converted to an estimated sea-surface height the height of the ocean surface above the seafloor.
The BPR water height resolution is 1 mm in water depths to 6, m, and the maximum timing error is 15 seconds per year. The station has two data reporting modes: standard and event. In standard mode, data are transmitted less frequently to conserve battery power. Event mode is triggered when internal detection software in the BPR identifies anomalous pressure fluctuations associated with the passage of a tsunami.
During event mode, all second data are transmitted for the first few minutes, followed by 1-minute averages. If no further events are detected, the system returns to standard mode after 4 hours. The two-way communication allows the TWCs to set stations into event mode in anticipation of possible tsunamis or to retrieve high-resolution second interval data in 1-hour blocks for detailed analysis, and allows near-real-time troubleshooting and diagnostics.
The data is also available on the NDBC website, and event data is highlighted when a system has been triggered. In addition, Figure 4. The central goal of the workshop was to determine an optimal network configuration that would meet multiple mitigation objectives, while addressing scientific,. To the extent that the constraints on siting can be quantified and the benefits expressed in functional form, array design can be approached as a problem in optimization.
Although the scheme was tested for only relatively simple cases, the methodology shows promise as an example of a scientifically robust process for siting and prioritizing stations in an operational sensor network. The technical memorandum provides a starting point for continued refinement of the siting decisions and extension of the DART array, if necessary, while also providing information to aid efforts by the international community to extend the network coverage.
The net result of the deliberations on the siting of the DART stations is the current array displayed in Figure 4. The prioritization of groups of these sites is presented in Table 4. Some of the more important issues involved in site selection are described in Box 4. The committee does not find any serious gaps in the geographic coverage of the DART network as designed, with regard to providing timely and accurate warnings and forecasts of far-field tsunamis on U. It can certainly be argued that denser coverage of open-ocean sensors would provide important redundancy capacity in light of current reliability problems discussed below and would provide more opportunities to improve the accuracy of model-generated wave forecasts.
From a more global perspective, gaps in coastal sea level station coverage as revealed in the Caribbean region, for instance; see previous section , which expose. TABLE 4. DART Array. Tsunamigenic zones. The likelihood that a particular fault zone will produce a tsunami is considered along with the coverage of the existing sea level network.
Seismic wave noise. If a DART is located too close to the seismic event that generates a tsunami, the shaking of the seafloor can cause spurious BPR fluctuations e. This seismic noise can be reduced significantly by locating the instruments no closer than 30 minutes of tsunami travel time from the closest possible source, after which time the seismic body and surface waves will have passed.
Timely signal. If the DART is sited too far from the tsunami source, too much time is lost between the seismic event, which is detected within a few minutes, and the arrival of an unambiguous sea surface disturbance at a DART site. In some locations, this consideration is more important than the seismic wave noise issue; DARTs have been placed as close as 15 minutes of tsunami travel time from the closest source.
Tsunami scattering. The presence of seamounts or other major seafloor features between a DART and likely tsunami sources needs to be avoided. These bathymetric features cause zones of shadowing or of reinforcement in their lee due to tsunami wave diffraction. To the extent that these effects are imperfectly represented in the tsunami propagation model databases on which the SIFT and EarthVu tsunami forecast systems rely, forecast quality will be adversely affected. Water depth. The acoustics communications device currently in use is rated to water depths up to 6, m, but the narrow acoustic beam requires the surface buoy to be closely held above the BPR.
Strong currents. Because of the need for a surface buoy, it is important to avoid strong current regimes, which could cause swamping or dragging of the buoy, or could make buoy maintenance difficult. However, the high cost of DART acquisition and maintenance may preclude any significant network growth. Looking to the future, the committee con-. Even though tsunamis do not occur frequently, redundancy in the array is still desirable. The surface buoy has two independent complete communication systems for full redundancy. In addition, in high-risk source regions, a certain amount of overlap in spatial coverage is desirable so that instrument failures may be partially compensated by having more than one DART in the region capable of providing a timely, high-quality signal.
Bottom roughness. For reliable communications, the BPR must be deployed on a reasonably flat, smooth seabed that will not produce scattering and interference of the acoustic signals. Although DARTs are typically deployed for two years, and have a design life of four years, there is considerable expense associated with deploying and maintaining them in remote regions.
For some sites, co-locating DART buoys with other buoy arrays might allow leveraging ship time and maintenance costs if there is no conflict with special DART requirements. Other considerations in choosing buoy sites include the difficulty or ease of obtaining permissions to enter other national EEZs Exclusive Economic Zones , shipping routes, seafloor infrastructure e.
These parameters of the DART network clearly deserve frequent re-consideration in light of constantly changing fiscal realities, survivability experience, maintenance cost experience, model improvements, new technology developments even new DART designs , increasing international contributions, and updated information on the entire suite of siting issues listed in Box 4. In addition, simulations of the effectiveness of the DART network, under.
The potential contributions of optimization algorithms to the design process have not been exhausted. A component of the periodic re-evaluations of the DART network needs to be the re-evaluation of the prioritization of each group of DART stations, not just individual stations, with detailed justifications for these determinations. In particular, the committee questions the rationale for the very low priority of the group of five DART stations deployed in the Northwest Pacific Table 4. The Kuril Islands in particular have been the source of numerous tsunamis large enough to invoke tsunami watches and warnings.
At the very least, DART stations covering the Kuril Islands would have a high value for the prevention of false alarms. A list of criteria might include:. Depending on the order of importance of criteria such as these, quite different prioritizations of the DART stations might result.
The value of the DART stations in the Northwest Pacific is primarily for the detection of medium to small tsunamis, in order to confirm that a large tsunami has not been generated and thus avoid the issuance of an unnecessary warning with its attendant costly evacuation. There are no serious gaps in the geographic coverage of the DART network as designed, with regard to providing timely and accurate tsunami warnings and forecasts for at-risk U.
However, the vulnerabilities of non-U. Recommendation: NOAA should regularly assess the numbers, locations, and prioritizations of the DART stations, in light of constantly changing fiscal realities,. Since the build-up of the DART network began in , it has experienced significant outages that can have adverse impacts on the capability of the TWCs to issue efficient warnings, to use near-real-time forecasts, and to cancel warnings when a tsunami threat is over.
The data loss also reduces post-tsunami model validation capability. Figure 4. The peaks in performance occur during Northern Hemisphere summer when maintenance is performed. Note, however, that the peak values in performance are decreasing with time as well. Maintenance occurs in the summer months, accounting for the annual cycle in Figure 4. The declining trend in performance is emphasized in Figure 4. A system availability of 69 percent is significantly below the network performance goal of 80 percent, which perhaps is not surprising for such a large, new, and admittedly hurriedly-deployed set of complex systems that are deployed in very harsh environments.
The issue of low network performance is exacerbated by the fact that clusters of nearby DART stations tend to be nonoperational for many months, leaving large gaps in DART coverage. For example, five stations cover the Aleutian Islands west of the Dateline, past the Kuril. Islands to Hokkaido. Although the Kuril Islands region produced many small basin-wide tsunamis over the past five years, all of these stations had failed by December , and four had failed in October , or earlier.
None were repaired until late June , after weather conditions had improved enough to reduce the risk of shipboard operations. The optimization scheme used for planning the locations of the DART stations and testing their ability to detect tsunamis basin-wide is based on an assumption of nearly percent performance Spillane et al. Given the current geographic coverage, the DART network is only useful for tsunami detection and forecasting if it is operational nearly percent of the time.
In a practical sense, when one DART station is inoperative, its neighbors on either side must be operational. If two neighboring DARTs become inoperative, then there must be an immediate mitigating action. Table 4. The committee has assumed that summer time maintenance cycles are, at least in large part, dictated by north Pacific weather. If this is the case, the maintenance of the high-priority DART buoys may not be practical or even possible.
The number of DART II system failures is higher than expected, with a current median time to failure of approximately one year when the design lifetime was four years Figure 4. To meet the mid deadline, the DART II was rushed to production and deployment without the customary level of testing required for a complex system like the DART, with its relatively extreme operational environment. This rapid deployment schedule required an active reliability improvement program, concurrent with initial operations and funding, to sustain effective operations while reliability improvements were defined and implemented.
However, budget cuts slowed both maintenance and reliability improvement. Furthermore, NDBC had no prior experience with seafloor instrumentation, acoustic modem. Department of Commerce Office of Inspector General, The report found that technology transfers from PMEL to NDBC have not been well coordinated and planned, and it offered several recommendations to address these concerns, such as ensuring that data requirements and technical specifications are clearly defined prior to the transition and that adequate funding is available to cover the transition costs.
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The report also recommends better coordination on research and development projects between the two NOAA centers to avoid duplication of efforts. By far the most common problem is mooring hardware failure. A system that requires unanticipated maintenance visits using costly ship time reduces availability of funds for other activities. The committee analyzed the benefits and disadvantages inherent in each of these maintenance approaches.
In order to maintain the current DART network configuration, adequate resources are needed for maintenance, including funding for unscheduled ship time to effect repair and replacement of inoperable DART stations. The alternative approach would be to invest the majority of resources into improving the DART station reliability to get closer to the. In this case, it must be understood and acknowledged that the DART network might be fully deployed but will not be fully functional until such time as the reliability of the DART stations gets much closer to the design goal of a four year lifetime than the present median time-to-failure of just over one year.
A partial amelioration of the draconian choices above could come from exploring new maintenance paradigms, such as 1 simplifying the DART mooring for ease of deployment from small, contracted vessels that are available, for instance, from the commercial fishing fleet and the University-National Oceanographic Laboratory System UNOLS fleet; and 2 maintaining a reserve of DART buoys for immediate deployment upon the occurrence of a significant gap in the network, weather permitting.
Since the build-up of the DART network began in , it has experienced significant outages that have a potentially adverse impact on the capability of the TWCs to issue efficient warnings, use near-real-time forecasts, and cancel the warnings when a tsunami threat is over.
Worse, multiple, neighboring DART stations have been seen to fail in the North Pacific and North Atlantic, leaving vast stretches of tsunami-producing seismic zones un-monitored. This situation persists for long periods of time. The committee considers it unacceptable that even a neighboring pair of DART stations in high-priority regions is inoperative at the same time.
Although an 80 percent performance goal may be satisfactory for the entire DART network, and for individual gauges, a much better performance is required for neighboring pairs of DART stations, especially in high-priority regions. Conclusion: Continued engineering refinements of the DART concept will allow NOAA to establish a more sustainable capability with reduced costs of construction, deployment,.
Recommendation: The committee encourages NDBC to establish rigorous quality control procedures, perform relentless pre-deployment tests of all equipment, and explore new maintenance paradigms, such as simplification of DART mooring deployment and maintaining a reserve of DART stations for immediate deployment. Conclusion: DART presents an outstanding opportunity as a platform to acquire long time series of oceanographic and meteorological variables for use for climate research and other nationally important purposes.
Potentially a DART buoy could also telemeter data acoustically from a seafloor seismograph although the demands on DART power would increase proportionally. The additional power requirements for acoustic and satellite telemetry would press the current design of the buoy thereby increasing risk to the primary goal of tsunami detection.
Nevertheless, broadening the user base could enhance the sustainability of the DART program over the long term and future designs should consider additional sensors. Chilean catastrophe.
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Architects and Engineers can learn a great deal from how buildings and infrastructure perform in earthquakes by visiting earthquake-stricken regions. The M8. Recognizing the impacts earthquakes may have on the Pacific Northwest, Reid Middleton had the opportunity to participate with the Structural Engineers Association of Washington SEAW reconnaissance team of engineers to observe and evaluate damage in the affected areas.
They worried more about where the press was in order to get attention. Now it is a professional procedure, with protocols. In a disaster, improvisation is the worst. The government of Chile did not have much information on how the international community was organised and worked. That has changed.
In the most recent earthquake, a new system of warnings was used to alert the population. Within minutes of the quake, downtown Coquimbo and its coastal areas were rocked by loud sirens. A convoy of ambulances, firefighters and police sought to accelerate the evacuation, as officers convinced reluctant homeowners to head for the hills.
Mobile phones were targeted with a series of tsunami warning messages, urging residents to abandon the coastal areas. The building can crack, tilt and even be declared unfit for future use — but it must not collapse. Discussing the earthquake, Felipe Espinoza, a Chilean firefighter, counts — on one hand — the multi-storey buildings destroyed. No multi-storey buildings are thought to have collapsed in the most recent earthquake. Four government officials were later charged with involuntary manslaughter. But there is another factor that has helped Chile to cope with powerful earthquakes — namely, the regularity of small-to-medium size quakes which do little damage, but serve to remind the public of the looming danger.