Smoothed Gridded Seismicity Effect for Land-Use Development, Case Study: Kalimantan Island, Indonesia

Smoothed gridded seismicity is an analysis model in seismicity that allows for the obtaining of a rate based on the b-value and the same magnitude range. The data study has been collected and analyzed from a background source gath-ered by PusGen, referred to as the PusGen catalogue, with approximately 70 thousand data points. Two software programs (i.e. USGS PSHA and OpenQuake) were utilized in this study, and both programs have been proven as reliable in the creation of the 2017 Indonesia Earthquake Hazard Map. The final steps are to compare the acceleration map results with the Kalimantan Island land-use map and to analyze suitability development planning against potential hazards and earthquake risks. The results stated that: (1) acceleration due to the shallow background earthquake for the Kalimantan region, range from 0.00-0.25g (using USGS PSHA) and 0.0-0.4g (using OpenQuake); (2) meanwhile, based on the deep background earthquake source, the maximum accelerations that occur are 0.15g and 0.25g when using USGS PSHA and OpenQuake, respectively; (3) the utilized of land-use for the current and future years is in line with the results of the acceleration simulation. The study recommends to take into account the seismic aspects in new planning of the capital city, mining and residential areas in order to reduce the existing risks.


Introduction
Smoothed gridded seismicity is one of the analysis models in seismicity that allows for the obtaining of a rate (namely a-value) based on the b-value at the same magnitude range. The variation of different earthquake events for each area is illustrated with different rate values. This rate is based not only on earthquakes in the selected zone area but also on their surroundings (Akinci et al., 2018;Hiemer et al., 2014). This method is applied to background earthquake sources. Background source is a term that refers to an earthquake source with no apparent or definite mechanism (Ghasemi et al., 2020;Irsyam et al., 2020). This study is limited to a magnitude of 4.5 <= Mw <6.5 for depths up to 50 km and the rest Mw> = 4.5. This assumption is in line with the calculation of earthquake background sources in Indonesia, especially in forming the 2017 Indonesian Earthquake Hazard Map PusGen, 2017;Syahbana et al., 2020). Smoothed gridded seis-micity is a method to complement the shortcomings of the area source method, which with the gridded method, divides the area into smaller ones to minimize the chance of seismic parameter errors in the specific zone. To conduct the smoothed gridded seismicity calculation, two software programs were utilized in this study. Both programs have been proven as reliable in the creation of the 2017 Indonesia Earthquake Hazard Map, i.e. USGS PSHA and OpenQuake and will be explained further in the method section. PSHA stands for Probabilistic Seismic Hazard Analysis, a method for calculating earthquake hazard that considers the probability of magnitude, distance and acceleration that may be exceeded. In this study, the PSHA is utilized on a time-independent basis, thus the probability of several earthquake scenario events can be combined without changing the initial probability, according to Poisson distribution Omang et al., 2016;Grunthal & Wahlstrom, 2001).
Kalimantan Island is one of the largest islands in Indonesia and has an excellent opportunity to become a destination for relocating the Indonesian capital city from Jakarta to Panajam Paser Utara and Kutai Kar-Rudarsko-geološko-naftni zbornik i autori (The Mining-Geology-Petroleum Engineering Bulletin and the authors) ©, 2021, pp. 115-126, DOI: 10.17794/rgn.2021.3.8 tanegara. In general, although this island only has a slight potential for earthquake hazard, its effects must be considered, especially if it is related to existing land-use and future development planning. The National Landuse Spatial pattern (Law Number 26 of 2007 Concerning Spatial Planning) has three parts: protection, cultivation and national strategic areas. The objectives of spatial planning for the national territory are to achieve several things, including: (1) national territorial space that is safe, comfortable, productive, and sustainable; (2) harmony between the natural and the artificial environments; (3) the integrated use of the land, sea, and air space, including space in the earth; (4) integration of spatial planning for national, provincial, and regency or city areas; (5) sustainable use of natural resources for the improvement of community welfare.
Continuing the spatial pattern of Kalimantan Island for the year 2028 is the distribution of spatial use in the form of protection and cultivation functions for the economic development of forestry, plantation, agriculture, and mining based on sustainable management with due regard to biodiversity. The spatial structure of Kalimantan Island is a hierarchical arrangement of urban-centres bound by an infrastructure system (transportation network system, telecommunications, energy, and water resources). Those urban-centres will be more scattered in the centre and along the coast of the island.
According to BKPRN (National Spatial Planning Coordinating Board) and President Decree No. 3 of 2012 concerning RTR for Kalimantan Island, until 2028, the island of Kalimantan will own 70 percent of the cultivated area, while the protected area will cover 30 percent of the island of Kalimantan. Cultivation areas will be spread out along the horizontal-axis island (west-central-east), while protected areas are spread north and south (see Figure 1). The spatial planning objectives for the development of the Kalimantan Island area: (1) "Lungs of the World" with the preservation of biodiversity conservation areas and protected function areas with vegetation of wet tropical forests at least 45 percent of the area of Kalimantan Island; (2) energy independence and national energy storage for electricity; (3) centre for the development of mineral, coal and oil and natural gas mining; (4) development centre for sustainable oil palm, rubber and forest product plantations; (5) the front border and gateway of the Republic of Indonesia with the State of Malaysia; (6) (7) development of tropical wet forest ecotourism areas and Kalimantan culture; (8) integration of intermodal transportation network systems that can increase inter-regional connections and open regional isolation; (9) self-sufficiency and national food storage. Future prediction, the eastern province, Penajam Paser Utara (North Penajam Paser) and Kutai Kartanegara region will be created as a new capital city to replace the role of Jakarta city (see Figure 2).
The development of land-use zoning is a crucial activity seen from various aspects, such as population density, economic equality, natural resources, including natural hazards in the form of earthquakes (Armaş,  . A background source earthquake as one of the earthquake mechanisms that is included in the above aspect. Therefore, as an improvement method to analyze this source (formerly area source), smoothed gridded seismicity is utilized to calculate the hazard in this area (Stirling et al., 2002;Werner et al., 2010;Zechar et al., 2013). Moreover, earthquake hazard analyses in Kalimantan Island are rarely done due to the small number of events recorded to date. Mistakes in considering some of these aspects will result in ineffective spatial planning or land-use objectives.
The novelty in this study is to analyze the region with a focus on the dominant earthquake source in the area, i.e. the background earthquake source. The challenge is how to make a background earthquake source to be used in analyses following the prevailing rules, starting with the declustering and completeness processes. In this study, a module has been made in Python to carry out this process to be further processed using OpenQuake software. Meanwhile, the USGS PSHA software is processed using the ZMap based on Matlab.
This study described the relationship between regional land-use planning with earthquakes, especially background earthquakes. In this paper, the authors divided the materials and methods into several subchapters, i.e. location, data, software used, and workflow. The location area study will be briefly explained correlated with seismicity conditions. Data used here was also described before and after the declustering process. Moreover, in this study, the software and workflow applied study is also being explained.

Materials and Methods
The area used in this study is 0.1 ° x 0.1 ° and uses a Gaussian distribution over a 150 km radius ( Smoothed gridded seismicity is a critical study that complements the previous method, which is considered more biased, namely the source area. In the source area, those boundaries of areas that are considered to have a homogeneous level of seismicity are still being debated because it is possible that these boundaries would be different for each researcher (Ide et al., 1996;Woo, 1996). Smoothed gridded seismicity analyses the area in small parts with different rates due to the earthquake background source.

Location
Kalimantan is one of the largest islands in Indonesia with coordinates between 4.836570° north latitude -4.876377° south latitude and 108.412472° -119.130835° east longitude. Kalimantan is an exciting location because this study area has essential national assets in mining, forestry, settlement, and even a discourse as a destination for moving the capital city of Indonesia in the future. Furthermore, this area has minimal earthquake sources compared to other locations in Indonesia. Indonesian locations, in general, have earthquake sources originating from faults, subduction, and megathrust. As seen in Figure 3, Kalimantan Island has an earthquake source dominated by the background. Therefore, this study will focus on the background earthquake to be analyzed using the two selected software programs. Additionally, an evaluation of the relationship between seismicity and land-use will be carried out to determine whether the development and land-use have been implemented correctly.
The Kalimantan island is composed of various bedrock, which are of continental, oceanic, and transitional origin ( To the north, the Kutai Basin is bounded by accreted crust from Tinggian Kucing (part of the Central Range) and bedrock from the Mangkalihat continent in its western and northern parts. The Tarakan Basin, which is further north than Kutai, is bounded by the accreted crust Dent-Semporna, Tinggian Sekatak-Berau, the basement from the continent of Mangkalihat. These basement terrane relationships are not fully understood. Some of these boundaries may be sutures indicating traces of collision zones or significant fault zones (Metcalfe, 1996;Van De Weerd & Armin, 1992). Earthquakes are relatively rare on Kalimantan Island. However, on June 5, 2015, an earthquake with a magnitude of 6 Mw occurred in the Ranau area, Sabah, which resulted in 19 fatalities, landslides on Mount Kinibalu and damage to buildings in the city of Ranau. Based on the Meteorology, Climatology and Geophysics Agency (BMKG) records, before the incident, an earth-   1964, 1982, 1983, 2000, 2006, and 2007. These earth-quakes had a magnitude above 5.0 Mw, and some tsunami followed. Shocks caused by the earthquake originating from the Mangkalihat Fault can impact the MMI VI-VII intensity scale. The VI-VII MMI intensity scale means that an earthquake that occurs can cause moderate to severe damage.

Data
The data collected to be analyzed in this study was data collected by PusGen, referred to as the PusGen catalogue (PusGen, 2017), with approximately 70 thousand data points. The data used is the magnitude of each earthquake and its location, depth and time of occur- , earthquake catalogues that have been relocated by (Engdahl et al., 1998(Engdahl et al., , 2007 and the catalog of relocated BMKG hypocenters of (Nugraha et al., 2018a). In Figure 4, there is a dominant source at a depth of fewer than 50 km, which is associated with the term shallow background. At a depth of fewer than 50 km, the existing earthquake sources consist of active and background fault sources. On the other hand, the number of earthquakes with greater depths appears small, less than 50 percent of the earthquakes recorded in this catalog. This phenomenon is caused by the source of the internal background earthquake comes from the Benioff zone.
This zone is a continuation of the megathrust/subduction zone where the mechanism is more internal to the continental crust, so it is often referred to as intraslab (Passarelli et al., 2018).
From Figure 5, the distribution of magnitudes in Indonesian regions in general can be seen. Earthquake events with varying magnitudes from 4.5 to 8 + Mw vary more at depths below 100 km, and a higher number is at magnitudes less than equal to 5.5 Mw for that depth. This occurrence indicates that many shallow earthquakes occur in Indonesia. In contrast, earthquakes with a depth of more than 300 km were also recorded here, but in small numbers.  Meanwhile, in Figure 6, the earthquake data recording before 1960 shows a small number and is limited to a magnitude greater than 6 Mw. After 1960, earthquakes occurred with a magnitude of less than 6 Mw were recorded at a significant amount. This finding is well correlated with the increasing sophisticated seismometer devices capable of recording earthquake energy to a minimum level (Nugraha et

Software
Two software programs (USGS PSHA and Open-Quake) have been proven as reliable in the creation of the 2017 Indonesia Earthquake Hazard Map (PusGen 2017). USGS PSHA is a software program released by the USGS (United States Geology Survey). In this program, several modules are used for seismic processing. There are also many modules in this program. For these purposes of study, a module that aims to create a background earthquake source is used to process the hazard calculation with a classical calculator for the PSHA.

Work steps
The work steps taken are as follows: (1) in Open-Quake, the catalog data obtained was first processed with a module made in Python language, including declustering, completeness, and rate calculation with a Gaussian distribution, continued by data processing via a classical calculator in OpenQuake; (2) in the USGS PSHA, the processed data was declustered using ZMap.
The rate was calculated using the agridMLsm module, and the acceleration value was calculated using hazgridXnga. The GMPE used is based on the logic tree utilized in the 2017 Earthquake map: Boore et al. 2014, Campbell Bozorgnia 2014, and Chiou Young 2014(3) The final step is to compare the acceleration map results with the existing spatial map of Kalimantan Island. This study analyzes the suitability of development planning against potential hazards and earthquake risk in discussion section.

Results
The data above is combined earthquake data foreshock, mainshock and aftershock. After declustering with the Gardner and Knoppof method (Gardner & Knopoff, 1974) and completeness (Nasir et al., 2013), the results are shown in the Table 1. From Table 1, the reduction due to declustering and completeness is considerable, even exceeding 50 percent. This finding is due to seismometer sensitivity and tectonic conditions in Indonesia, which may differ from other regions.
The analysis using OpenQuake and USGS PSHA software can be seen in Figures 7-10. Processing at the USGS PSHA begins with preparing background earthquake input by dividing the mainshock earthquake source into six depths (0-25, 25-50, 50-100, 100-150, 150-200, and 200-300 km). Subsequently, smoothing gridded seismicity was carried out with the Gaussian function, which considered the effect on the surrounding grid with a distance of up to 150 km to calculate the rate on those grids (Frankel, 1995;Petersen et al., 2008). Then, the acceleration value was calculated based on the  current rate using existing attenuation equations and individual weights deemed appropriate to Indonesian conditions. It can be seen from the shallow earthquake analysis that there are zones that are centered on several areas, such as in the eastern part of East and South Kalimantan and the western part of West Kalimantan. Meanwhile, in other areas, there is no significant acceleration value.
The acceleration caused by the deep seismic mechanism presented in the Figure 8 shows us what it looks like on the east side, in either East or South Kalimantan Provinces.
There is no significant difference between the deep background earthquake source acceleration values from two software programs, as depicted in the Figure 10. In the results, OpenQuake was formed on the eastern side of East Kalimantan and part of Central Kalimantan and South Kalimantan's border. Meanwhile, the USGS PSHA was formed in the same area, but the coverage area is more extensive than OpenQuake.

Discussion
The exciting findings from Figure 8 can be observed here. This phenomenon is quite questionable due to the absence of a well-identified Benioff zone around Kalimantan Island's eastern side. There is a suggestion about this condition that it could be due to the earthquake source on the farther side, namely north of Sulawesi Island, or other mechanisms caused by fluid activity under the crust (White et al., 2019; Zhao et al., 2017).
By using OpenQuake software, the results of the acceleration calculations are more extensive on the same side as those calculated with USGS PSHA (see Figure  9). The pattern that is formed also has similarities in the area where the acceleration parameter increases. This result is reasonable because there is a bias in the numerical process carried out by Python and Fortran, coupled with the interpolation process in contour formation.
Based on the simulation results of the earthquake acceleration and spatial planning and Kalimantan Island area, the various conditions that exist can be seen. First is a discussion of shallow and deep background earthquakes. A shallow background earthquake is an earthquake that is influenced by an unclear mechanism with a hypocenter depth of fewer than 50 km, and a deep background is the result of Benioff's source being at a deeper depth of up to 300 km Syahbana et al., 2020). The calculation shows that the highest acceleration value is in the eastern edge of East Kalimantan Province. Meanwhile, there is an acceleration of 50 percent of the maximum value in West Kalimantan Province for shallow sources and Central and South Kalimantan for deep sources in other areas. It can be seen from Figures 7-10 that the shallow background earthquake sources dominate the study area more than the deep one. This fact is evident from the seismotectonic Kalimantan region, which has none of the Benioff zone around it. The closest Benioff zone in the Kalimantan area is north of Sulawesi Island. Second is a discussion of spatial planning on the island of Kalimantan in the present and in future conditions. In the explanation found in the previous chapter and as seen in Figure 1, the National Spatial Planning Coordinating Agency states that the East Kalimantan province on the east coast is used for forestry and mineral mining, and the south and central borders of the Kalimantan provinces for forestry and agriculture. Lastly, the west coast of West Kalimantan is used for natural tourism parks, forests, and settlements.
Moreover, substantial attention is given to the mine planning on the east side due to an earthquake with an acceleration on the bedrock of 0.4g and the residential side with a maximum acceleration of 0.2g. According to the planning of the capital city relocation, from the earthquake hazard side, those areas are predicted to experience an earthquake acceleration of up to 0.1g, as described in Figures 9 and 10. According to Trifunac & Lee (1992), this site will experience shaking, as previously mentioned, at level VI of MMI. Furthermore, the cause of that needs some engineering countermeasure so that the infrastructure will remain during a hazard. According to the National Board for Disaster Management (BNPB in Indonesian), losses due to the earthquake during 1815-2019 regarding earthquakes reach USD 3382. This number is quite enormous in such an area with a sparse population (BNPB, 2021). Furthermore, based on a national discussion organized by the Ministry of National Development Planning / Bappenas with the title "Towards a Future Capital: Smart, Green and Beautiful," then if there is a planning failure in relocating the capital city, it will endanger around 15,801,800 people (not including those who move from outside Kalimantan) and a financial loss of at least USD 32.9 billion. As a result, serious attention needs to be emphasized on slope stability, whether in closed or open types, building structures, and the types of materials available for settlements Umar et al., 2014). Based on the lowest fatality earthquake, which is suspected to be due to the material of a common village house called "Lamin" (Fajarini & Ratniarsih, 2019;Mulyoutami et al., 2009). This house is made of wood, while wood itself is well-known as a good material to absorb impulse energy, such as an earthquake. Apart from that, modern development in society will always occur, including house models and material changes. Recently in Indonesia, homes have been constructed from brick and concrete. Since these buildings behave differently when exposed to earthquake energy, it is necessary to design and plan the construction of earthquake resistant buildings. A further problem that needs to be taken into account is the propagation of earthquake waves from the bedrock to the surface, often termed wave propagation. This wave propagation will result in an amplification or deamplification event, namely an enlargement or reduction of the acceleration value. To carry out this study, it is necessary to also examine the site class on Kalimantan Island, as a whole, using the Vs30 parameter as regulated in the Indonesian National Standard (SNI) for geotechnics and SNI for Building Planning against seismicity. Vs30 is an engineering parameter that shows the average shear wave velocity from the ground to a depth of 30m. This parameter is one of the essential variables in seismic analysis, one of the examples is related to the amplification of acceleration, Based on the results of this study, it is also recommended to analyze other models to predict the level of earthquake activity, for example, using the Markov Chain model that has been applied to the Algerian region (Dahmoune & Mansour, 2018). Thus, the level of earthquake activity with several models can be observed to obtain a more comprehensive understanding. Meanwhile, land-use for forests and agriculture does not require serious attention due to earthquakes, except this region located in a hilly area.

Conclusions
Seismic studies associated with the evaluation of the spatial land-use of an area are vital. In this study, a seismic analysis was made with a 2 percent return period exceeding 50 years using two open source software programs. This study involves a background earthquake source, which is the dominant earthquake source on the island of Kalimantan. Both software programs show several zones with a maximum acceleration in Kalimantan Island's east and west areas. Shallow background results in higher acceleration than deep ones. Using OpenQuake, the acceleration value is up to 0.2g on the coast of West Kalimantan and 0.4g on the east coast of East Kalimantan, whereas USGS PSHA calculated only 0.1g and 0.25g for the respective area. The area is planned to be a new capital city, mining and residential area, while the areas with a lower acceleration are used as plantation and forestry areas. According to the MMI scale, the new planning capital city will be up to about 0.1g in acceleration or level VI. Therefore, it is necessary to conduct a more comprehensive study in the planning of the new capital city, mining and residential areas by considering the potential hazard of earthquakes based on the available data.