Exploring key issues related to tsunami shelter in Padang city – Indonesia

. Padang is a city on the coast of Sumatra island in the province of West Sumatra that has the potential to be threatened from a tsunami originating from the Mentawai megathrust. Various attempts have been made by the Padang City Government to anticipate casualties if a tsunami really occurs. One such effort is in the form of building shelter or TES (Temporary Evacuation Sites). Unfortunately, until now the data on the capacity of existing shelter and the number of shelter needed have not been found. In addition, the maintenance of existing shelters has the potential to become a burden on the Padang city government budget. The Mayor of Padang once complained about the need for the budget to build and maintain the shelter building so that it could function properly when needed. Therefore it is necessary to conduct a study regarding the optimal amount of shelter and how to optimize its function. Determination of the optimal number of shelter begins by identifying factors that influence the determination of the location of the shelter through questionnaires and interviews. This study also examines the alternative use of shelter and maintenance techniques so that the constructed shelter can be effective and efficient according to its function but still economical or not a burden on the government budget.


Introduction
Padang is located in the West Sumatra province of the island of Sumatra.Subduction of the Indian-Australian plate beneath the continental Eurasian (Sundaland) plate at a rate 7 cm/year with N20 azimuth, down the Sunda Trench (Minster and Jordan, 1978;De-Mets et al., 1990).Oblique subduction at about 45 has resulted in two significant faults that are parallel to and lie between the trench and volcanic arc.The vertical Sumatran (Semangko) Fault marks the boundary between the Eurasian (Sundaland) plate and the majority of the volcanic arc to the northeast with a forearc basin to the southwest, while the Mentawai Fault (Kemal B.M., 1993) separates the forearc basin from a forearc accretionary ridge complex further southwest.The entire forearc sliver between the trench and the Sumatran Fault is decoupled and moves northwestward.
Some areas of the city of Padang in the form of a plain with a slight slope to the east.But in some areas that are almost flat, there are more than half of the city's population.With a population of 914,968 (BPS, 2016), 508,804 of them are in the tsunami red zone (BNPB, 2010).Padang City has a population of 914.968 (BPS, 2016).508,804 of them inhabit the tsunami red zone (BNPB, 2010).The tsunami red zone is a zone that is predicted to be hit by the tsunami.With the large number of people inhabiting zones that have the potential to be threatened by the tsunami, the government needs to think of efforts to save these threatened populations, for example by providing facilities for vertical evacuation.Vertical evacuation is believed to be a preferred mitigation, because the effective time available to do so is very little, which is 17 minutes (Kemal et al, 2017).But until now in the city of Padang only four official buildings were built as TES (Temporary Evacuation Sites).
The objective of this study is to identify and explore key issues related tsunami shelter in Padang.

Tectonics Setting of Sumatra
Sumatra island where the city of Padang located is part of the Eurasian tectonic plate which collides with the Indo-Australian plate.As a result of this collision, the Indo-Australian oceanic plate goes down Sumatra.The tectonic conditions in Sumatra then led to the emergence of megathrust in the form of accretionary prisms that emerged as non-volcanic islands in front of Sumatra such as Simeulue, Nias, Siberut, Sipora, Pagai, Enggano and others.This Megathrust later became the source of a powerful earthquake above 7.0.These earthquakes in the megathrust area usually have very shallow depths.Because of that it has the potential to cause a tsunami.Some powerful earthquakes that cause tsunamis are shown in the following Fig. (Fig. 2).In Fig 2 it can be seen that there are two segments in the Mentawai archipelago, namely the Siberut and Sipora-Pagai segments.In the Siberut segment in 1797 there was an earthquake measuring 8.7-8.9 magnitude.Then in 1833 in the Sipora-Pagai segment there was a very strong earthquake measuring 8.9 magnitude.Both the earthquake in the Siberut segment and the Sipora-Pagai segment caused a tsunami (Borrero et al., 2009).In the Sipora-Pagai segment, a very strong earthquake was repeated successively on September 12, 2007 with a strength of 8.4 magnitude and on September 13, 2007 with a strength of 7.9 magnitude.Both earthquakes in the 2007 Sipora Pagai segment did not cause a large tsunami, except only a small tsunami (Borrero et al., 2009).Fujii & Satake (2008) stated that the tsunami height was approximately 1 meter in the city of Padang.While the tsunami that occurred in this segment in 1833, also in the Siberut segment in 1797 was large (Natawidjaja et al., 2006).1797 caused an earthquake measuring 8.7 -8.9 magnitude has not yet repeated a return period, except for the earthquake that occurred on 30 September 2009 with a strength of 7.6 magnitude (USGS, 2009).
With this magnitude 7.6 earthquake occurring, many experts said that the stored energy was still two-thirds more in this segment, which could cause an earthquake of magnitude 8.6 or even more (McCloskey, 2010).

TES (Temporary Evacuation Site): tsunami shelter
TES is a building that can be used to vertically evacuate multi-storey buildings.The high inundation of sea water that rises to land in the event of a tsunami according to Latif's prediction (2018) is 4.7 meters.Meanwhile, megathrust in the Siberut segment in Methodology In order to collect data for this study, an FGD (Focus Group Discussion) has been conducted in Pusdalops UPT BNPB Padang, attended by experts and activists in disaster reduction in Padang and West Sumatra.In addition, Padang surveys were also carried out to temporary evacuation sites, namely four special evacuation sites built by the government (BNPB) This FGD invited competent speakers in the field of disaster, especially the tsunami and BPBD Sumatra Barat (Badan Penanggulangan Bencana Daerah-West Sumatra Regional Disaster Management Agency) institutions as competent and responsible for disaster risk reduction efforts, including facilitating the construction of TES.

TES in Padang
Aware of the threats that come from the Siberut segment megathrust, the Padang city government has made various mitigation efforts.One such effort is to design and realize the establishment of TES (Temporary Evacuation Site).TES is a vertical evacuation place in the tsunami red zone.At present the government has built four TES, namely in the Ulak Karang, Komplek Jondul Kelurahan Parupuk, Lubuk Buaya and Shelter Darussalam Kelurahan Tabing areas.
As for official TES: it has a considerable capacity.Then it is also equipped with public kitchen facilities, bathroom and toilet.In addition to these four official TES units, there are also a number of government buildings that has also a function as TES.These buildings were built after a strong earthquake 29-09-2009.In addition, there are also a number of private-owned high-rise buildings which are expected to function as evacuation sites from the tsunami.These buildings are multi-storey where the height of the floor is at least 10 meters above sea level.The following table is a government-owned and private building that have dual function as an evacuation site All buildings mentioned in the table above have not been verified as being feasible in their strength against earthquakes that precede the tsunami.It can be reduced after verification.These buildings are not specifically planned for evacuation sites.Therefore the government must make a Memorandum of Understanding (MoU) with building owners.If a MoU has been made, then special access will be built such as an external ladder that allows people to evacuate to the building, both on weekdays and outside working hours and holidays.

Key Issues of TES needs in the city of Padang
There has been no research that can determine the number of official TES needed by people who are potentially affected by the tsunami in the red zone.
Research on this number seems to be necessary, related to the estimated number of people who need it.Previously, people who were prioritized for vertical evacuation using TES were needed.
Priorities for using TES are elderly parents, pregnant women, children and people with special needs.The rest is assumed to be able to evacuate horizontally to the east to a minimum altitude of 10 meters above sea level.In the city of Padang there is a special sign made on the highway, which is a sign that says a safe border from the tsunami.Based on the table above, the capacity of multistorey buildings that can be used for communities threatened by a tsunami is sufficient.Because, part of the threatened community in the tsunami red zone is expected to choose, or it is recommended to choose horizontal evacuation.But the amount is not enough if the Padang city government has not yet entered into a MoU with building owners.Then the amount can be insufficient if after assessment of building construction there are buildings that do not meet earthquake-safe building regulations (building code).Therefore, it can be ascertained that a new evacuation building is needed, which meets the building standards for earthquake safety and tsunami safety, and can function optimally with various functions or uses.Because, in some urban areas there are no multilevel buildings either government or private in the red zone of the tsunami.

Current condition of TES
Of the four existing (official) TES, it has not been used as expected.In general, all of these shelters have not been properly managed.Of all the assessments given by FGD participants, they can be grouped into five categories as follows.1. Benefits: This TES has not provided maximum benefits to the community.As stated by Martios Alius, the person in charge of the TES in Ulak Karang Padang; "This TES is just waiting for the tsunami to come.It does not function for social activities.This happened, because before the construction, the community was not invited to discuss about the management plan and utilization of the TES.While the cost of this TES is expensive".Januar, an activist from the KSB (Disaster Preparedness Committee) said: "TES is used for useful activities such as sports, but often also used by some young people to date.So, the utilization is not maximal ".Yenni Yuliza also stated: "Existing TES can be used as a village office so that it can provide maximum benefits".2. Maintenance of buildings: It has not gone well.
Dr. Eva Rita stated as follows: "There are about 30% of the people who do not know the TES, the buildings they see every day.This is surprising.There are also some people who feel they don't need TES.They were quite resigned to facing the tsunami.Then, the Chairperson of the RT (Neighbourhood leader) and Chair of the RW (Commune leader) as the local leader in the TES location is located, it should have a maximum function in the use and management of TES, both for daily use and when needed at night evacuation".Syafrimet, a disaster risk reduction activist from Jemari Sakato (NGO) stated that the community's understanding of the threat of disaster was still lacking.He said: "It is necessary to continue educating the public so that people are aware of the disaster.Furthermore, people who are aware of the disaster will later be aware of the need for a TES and can participate in maintaining it".Meanwhile Edi Hasymi, the head of the Padang BPBD implementation admitted that the treatment of TES was not maximized, because of the four TES buildings, only two had been handed over from BNPB to the Padang city government.As stated: "TES maintenance has not been fully carried out because not all TES buildings have been handed over to us.Two buildings that have been handed over have been formed by the management ".

Feasibility of TES:
The feasibility of TES as a place for evacuation from the tsunami is still considered less feasible.Because, the facilities available in the TES building are still not as they should be.Patra stated as follows: "In a TES there must be a logistics warehouse to store only food, drinks or other important necessities needed by the people who take refuge there.In addition, there must be a KSB in each TES.Whereas currently KSB is only available at the village level.TES buildings also should not be too close to the beach to avoid grinding the foundation of the building by a tsunami.In addition, schools or communities near a TES building must have plan B if the TES turns out to be collapsed by an earthquake".Yenni Yuliza also stated: "Access to TES must be open to the public".

Capacity:
The capacity of TES and multi-storey buildings that can be used as evacuation sites from the tsunami is not sufficient.To calculate the TES requirements related to its capacity, it needs to be done carefully, as stated among others by Eliyusman: "It is necessary to count the population in various circumstances, for example the number of residents day and night, and between workdays and week-end.This is all related to the shelter capacity needed ".

Responsible officer:
Although in the two TESs that have been formally handed over, the management has been formed, but it turns out that responsibility has not yet proceeded as it should.The proof is that there are TESs that are used by some young people to carry out activities that are not useful, such as dating.

Conclusion
1. Padang has a large population threatened by a tsunami.2. Although a portion of the population in the tsunami red zone will evacuate horizontally away from the coast, walking towards the east, but the capacity of multi-storey buildings in the red zone is not comparable to the population requiring vertical evacuation.Especially when compared to official TES 3. From official TES, utilization has not been maximized.From the FGD and the investigation at the TES location, it was found that the TES that only functioned as an evacuation site looked like less useful 4. With the plan to continue to realize the TES in accordance with the amount needed, then in the future TES must function double or multiple

Table 1 .
Government and private buildings that also function as TES(BPBD Sumbar, 2018)