Essay: Unlocking the Potential of Macroseismic Intensity Data with Shake Map Usage



Paste TASK 1

Macroseismic intensity data is a method for determining the shaking pattern and damage extent of an Earthquake. It describes the complexity of ground motion variations on instrument recordings like seismic intensity maps for the 1994 Northridge, California Earthquake. It is useful for communicating with public, media, earthquake response. It also helps in reconstruction of shaking distribution for Shakemap Atlas, PAGERs EXPO-Cat. The regression relationship between Modified MercalliIntensity and PGS were developed based on taking intensity value from a map at the strong motion location. For each station, the nearest intensity value is selected. Incase, if it is not within 3 km, then the strong motion data is not used for correlating. Seismologists are working with Peak ground values, rapid loss modelling uses macroseismic data as the hazard input like PAGER for response, QLARM for mitigation and response and ELER. USGS and DYFI system have available intensity data for detecting of intensity variability in a region.

The intensity attenuation with distance was defined in terms of epicentral intensity. The relationships are used to generate maps of estimated shaking intensities within a few minutes of events. The correlation between Imm and PGA is Imm= 3.66 log(PGA)-1.66

The correlation between Imm and PGV is Imm= 3.47 log(PGV+2.35). The TriNet correlation of ground motions. Imm=2.20 log(PGA)+1.00.

To improve the state of art in development of GMICEs, Homogenized global dataset should be accumulated by applying selection criteria. A standardized data analysis should be applied to derive reversible conversion relationships for a new global GMICE. Then global GMICE relationship should be compared to actual relationships. To homogenize the datasets, larger PGM value between two horizontal components should be considered. Macroseismic intensity 2 is the lowest intensity allowed. The distance between macroseismic observations and ground motion should be less than 2km. The hypocentral distance of seismic station should be less than 200km. The limitation of GMICEs is that they only consider only ground motion to intensity estimates. In shakemap intensity estimation, GMPEs are used to determine PGA and PGV whereas GMICEs are used to convert PGA and PGV into intensity. The global availability and invertible GMICE availability is helpful for upgrading the intensity and PGM datasets in regions of low seismicity.

The European Macroseismic Scale (EMS-98) is the seismic intensity scale for assigning seismic intensities in European countries. It is the first intensity scale use by Seismologists. It is used to evaluate the intensity assessments. The macroseismic intensity is used EMS-98 in the severity of ground shaking. It denotes how an earthquake affects a specific place.

Seismic Zones could be of 3 things. A region map in which a common level of seismic design is required. This is Obsolete. A region map in which a common areal rate of seismicity for the purpose of calculating probabilistic ground motions. Building code maps using numbered zones 0,1,2,3,4 are practically obsolete. These are derived from probabilistic ground motions. These are included in the seismic provisons of U.S. model building codes.

Task 3

Shake Map is a tool used to portray the extent of potentially damaging shaking following an earthquake

It can be generated for both small and large earthquakes in areas where it is available. It can be used for emergency response, loss estimation, and public information. Shake Map was first developed for earthquakes in southern California as part of the TriNet Project, a joint effort by the U.S. Geological Survey (USGS), California Institute of Technology (Caltech), and the California Geological Survey (CGS).

Now older analog instruments were replaced with a state-of-the-art seismic network with digital communications in real time. This network enables seismic data to be used in new and innovative ways. A product of the new network, Shake Map, was made possible by advances in telecommunications and computer-processing speed, and research aimed at understanding the relation between recorded ground motions and damage intensities. Shake Maps show the distribution of ground shaking in the region, information critical for emergency- by the earthquake

Where is less damage? What resources must be mobilized and in what quantities? Government response organizations typically answer these questions after a preliminary survey of the damaged area. Private-sector organizations conduct their own investigations but also wait for government reports regarding damage.

This reconnaissance requires hours and sometimes days to complete. As a result, decisions regarding search and rescue, medical emergency response, care and shelter for the injured and displaced persons, and other critical response needs must often be made while information is still incomplete.

In the past, rapidly available information on an earthquake included the magnitude, location, and some assessment of the probability of damaging aftershocks. Even though useful, this information was not sufficient to support rapid post-earthquake emergency-management decision-making. Because an earth- quake happens over a fault surface, not at a single point, the location of the earthquake (the epicenter) tells us only where the earthquake started, not necessarily where the shaking was the greatest. For a large earthquake, damage can sometimes occur hundreds of miles from the epicenter. Other factors, such as rupture direction and local geology, influence the amount of shaking in a particular area.

Although emergency responders identified many areas of heavy damage soon after both the 1994 Northridge and the 1989 Loma Prieto earthquakes in California, additional regions of severe damage were only belatedly discovered. A Shake Map displays the distribution of ground shaking within minutes after an earth- quake so that emergency services may be deployed to those locations.

Shake Map s rapid portrayal of shaking distribution following an earthquake provides opportunities to enhance post-disaster response by integrating other useful technology including geographic information systems (GIS) and the Federal Emergency Management Agencyʼs (FEMA) loss-estimation software (HAZUS). City, county, and State agencies can obtain Shake Map “shapefiles” for use as overlays with GIS, providing a more detailed under- standing of potential damage to local infrastructure and facilitating a more effective response. HAZUS estimates economic (damage and dollar losses) and societal impacts (number of casualties, displaced families, shelter needs) of earthquakes.

Though initially developed primarily for emergency management, Shake Maps have been shown to be highly beneficial for other user sectors. These other uses include improved loss estimation, public information and education through the media and webpages, financial decision making, and engineering and seismological research. Some specific examples are provided below for these use cases.

Current work will soon enable users to have automatic delivery of a wide range of Shake Map products with a variety of types of telemetry, including wireless devices. Coupling automatic Shake Map delivery with instant analysis of the user s facilities will allow immediate impact assessments, enabling rapid response decisions to be made more easily and confidently.

For potentially damaging earthquakes, Shake Map produces response spectral acceleration grid values for three periods (0.3, 1.0, and 3.0 sec). The spectral acceleration values are used for loss estimation, as mentioned above, yet these measures also serve many earthquake engineering analysis purposes. In a post-earthquake environment, information from engineering analyses of structures (including via Shake Cast, see below) provides a framework for post-earthquake occupancy, tagging, and damage inspection by civil engineers.

The effective reduction of the impact of future earthquakes is, or at least should be, one of the primary targets in Greece, a region of intense seismic activity. A national seismic hazard mitigation program, in order to be realistic, should have the following steps, fulfilled over different time scales:

Long term stage: This time scale is usually of the order of decades and the main target is to improve the Building Code, and at a second stage the land-use regulations. In Greece, the currently applied building code is the “Hellenic Building Code” e.g. EAK (2003).

Medium term stage –The stage of preparedness: Over time scales of few years, national measures should be taken aiming at preparing for possible earthquakes. In this stage, for example, all the methods that concern the simulation of expected ground motion in urban regions should be taken into account. These scenario earthquakes provide the means to evaluate in advance the level of shaking in a specific urban region (for the region of Greece

e.g. Benetatos and Kiratzi, 2004; Roumelioti et al., 2004; Theodulidis et al., 2006). Moreover, at this specific stage of preparedness, the evaluations of the time – dependent earthquake predictability models should also be considered, taking into account the uncertainties of the methods.

Short term stage: At this stage, with time scales from months to days, accurate predictions would be required, but as we must all admit, for the time being, the seismological community is still very far from this target. Thus, we must focus our attention to best dealing with the aftermath of an earthquake, and this is the main subject of the present paper.

After the earthquake: Following the occurrence of a strong event it is required to have the source parameters of the event and to identify the areas of strongest shaking. At this stage, we are not talking about a scenario event as in the previous cases, but we have an event, where seismologists will be asked to provide shake maps as soon as possible.

Here, we present an information system tool – called hereafter “SEIS-MOTION”- which was installed in order to compute, in near-real time, the moment tensor, the finite fault slip models and provide shake maps after the occurrence of strong and moderate size earthquakes in Greece. The system operates through the Seismological Network of the Aristotle University of Thessaloniki (AUTH), as this is maintained by the faculty and staff of the Dept of Geophysics.

“SEIS-MOTION” offers important information beyond magnitude and location of an earthquake by depicting the geographic distribution of the strongest ground shaking within a time interval which is much shorter than the one required for in-situ reconnaissance. From an emergency management perspective, although this information can contain significant uncertainty (as it is based on synthetic values in the near-field of the earthquake), it is preferable to make decisions based on some scientific results than on guesswork or even rumors in some cases.

References

Benetatos Ch. & Kiratzi A.A (2004). Stochastic simulation of intermediate depths earthquakes: The cases of May 30, 1990 Vrancea region (Romania) and January 22, 2002 Karpathos (Greece) deep focus earthquakes, Soil Dynamics and Earthquake Engineering, 24, 1, 1-9.

Benetatos C., Dreger D. & Kiratzi A (2007). Complex and segmented rupture associated with the 14 August 2003 (Mw 6.2) Lefkada (Ionian Islands) earthquake, Bulletin of the Seismological Society of America, Vol. 97, No. 1B, 35–51, doi: 10.1785/ 0120060123.

Dreger D. S (2002). Time-Domain Moment Tensor INVerse Code (TDMT_INVC) Version 1.1, Berkeley Seismological Laboratory, 18p. Dreger D. S (2003). TDMT_INV: Time Domain Seismic Moment Tensor INVersion, International Handbook of Earthquake and Engineering Seismology, W. H. K. Lee, H. Kanamori, P. C. Jennings and C. Kisslinger (eds.), Vol. B, 1627p.

Wald, D.J., Earle P., Allen T.I., Jaiswal K., Porter K. and Hearne M.(2008)

Grunthal G 1998. European macroseismic scale 1998(EMS-98)

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